TroubleShooting BGP Routing Issues

                         Let’s now consider common BGP Routing issues for example, we might have incorrect network statement, let’s double check to make sure that we have enter the network statement correctly, let’s make sure that we haven’t transpose to couple of numbers in the IP Address in the example but something that bit more unique to BGP is a concept of the “Next Hop Router”

                           A big point to keep in mind is that when “an advertisement comes into Autonomous System and it’s advertised over IBGP connections to Routers all belonging to the same Autonomous System, by default the next Hop Router information is not updated” and it’s possible that we got a Router residing in this Autonomous System that has a no way to get to the next Hop Address that’s been advertised to in this BGP advertisement.

                            One way we could address that is to “Redistribute BGP into the IGP”, we could alternately set up the static Route to tell the Router how to get to that Next-Hop-Address however, we could go into the BGP Router Configuration of a Router and say “Neighbor” and then we give the neighbors IP Addresses or Peer Group name and then we say “Next-Hop-Self”

                           It’s going to cause a Router to advertise its IP Address as the Next Hop IP Address when it’s sending a BGP Routing update to an IBGP neighbors, those are few different ways we might be able to address an issue where a Router within an Autonomous System is not able to reach the next Hop Route advertised into BGP Advertisement.

                            Similar to EIGRP we could have a Split-Horizon issue which say’s if a Route was learned on an interface that interface is not going to advertised the Route back out and in a point to multipoint network maybe like frame-relay that could be an issue.

                    We could have Filtered Routes, we might be doing some Route Filtering maybe intentionally or maybe there is more believable Route like a Static Route in IP Routing Table and it’s possible that BGP is taking a Sub Optimal Route because of Inappropriate path Attributes

                     Infect to illustrate that bit further, let’s go out to interface and Troubleshoot a very real world issue when you got an enterprise network connected out to more than One ISP and by default we are taking a sub-optimal path and let’s see how to fix that.

                   Notice that Router R2 has a connection of 768K out of ISP1, it’s got a 1.544Mbps connection out to ISP2 and clearly, we would prefer to use the ISP that had a highest bandwidth we would prefer to use ISP2, let’s see what we using right now though, if we do a

Ø  R2#show ip route

                          I am using 9.9.9.9 as an example, of some internet destination, that’s actually a Loopback interface on my INET Router on picture, and it looks like to get there i am gonna go via 198.51.100.2, that’s actually ISP1 that’s the slower link and why is that? let’s take a look at BGP Table.

Ø  R2#show ip bgp

                     BGP knows about two different ways to get there it knows that we could get there via ISP2 or ISP1 but notice the (greater than >) sign, this is telling us that we were using ISP1 and that’s this enterprise network Autonomous System 65001 as it going out to the internet, how does it look from the internet as coming back in, let’s go to the INTERNET Router and let’s do a

Ø  INET#show ip bgp

                      Let’s look at one of Routes inside the Enterprise Autonomous System, 192.0.2.0 as an example, i can get their couple of different ways but notice the Greater than “>” sign is it looks like from the prospective of the internet we gonna go via ISP1 again we going via the slower link and underline causes most likely a lower Router ID(Next Hop Address) and in the Real World, we probably not gonna be able to do any work on the ISP Router we have to do our work on Enterprise Router in this case Router R2, and we want to be able to do Configuration just on R2 to influence both Outbound and Inbound Path Selection.

                      To influence the Outbound Path Selection let’s use the Local Preference, notice that we do not currently have a Local-Preference set for Routes that we learned via the ISP1 and ISP2 Routers, let’s change and Higher Local Preference values are preferred, to do this we create a couple of Route-Maps. I am gonna create a Route-map for ISP1

Ø  R2(config)#route-map ISP1

Ø  R2(config-route-map)#set local-preference 100

                             I am going to apply this to Routes that I am learning from ISP1, let’s create another Route-Map for ISP2 and i am gonna set the higher Local-Preference value to make it more preferable

Ø  R2(config)#route-map ISP2

Ø  R2(config-route-map)#set local-preference 200

                          Now to make this take effect we have to apply the Route Maps as a part of the neighbor statement in Router Configuration mode for BGP

Ø  R2(config)#router bgp 65001

Ø  R2 (config-router)#neighbor 198.51.100.2 route-map ISP1 in

                         I want to apply that in Inbound direction another word, as i learned Routes from that neighbor, i want to apply the ISP1 Route-Map which is going to assign those Routes to a local Preference of 100, let’s do something similar for the other neighbor for ISP2.

Ø  Router(config-router)#neighbor 198.51.100.6 route-map ISP2 in

To make this take effect, let’s reset the BGP Process

Ø  R2#clear ip bgp * soft

Ø  R2#show ip bgp

                      And look at this now in order to get to this 9.9.9.9/32 network, we gonna go via ISP2, notice the Greater than “>” sign why is that?

                       It’s because of the Local-Preference there is a Local-Preference of 200 to use ISP2, there is a Local-Preference of 100 use ISP1, we’ve now influenced Outbound Path Selection to prefer the ISP that has more bandwidth however, we now need to Influence Inbound Path Selection, host out on the internet are still coming into us based on the shortest Autonomous System Path so, let’s do this.

                         Let’s say that we want to Prepend to that Autonomous System Path some additional Instances of our own Autonomous System, that’s what i mean, let’s create another Route-Map

Ø  R2(config)#route-map ASPATH

ü  This is name, i made up that’s not some sort of Cisco iOS Keyword

I am setting the Autonomous System Path Attribute such that, i am prepending additional instances of the local Autonomous System, i am gonna add couple of additional instances

Ø  R2(config-route-map)#set aspath prepend 65001 65001

                              And i am only going to apply this Route-map to ISP1, ISP1 is going to appear to have more Autonomous System to transit in order to get into the Enterprise Network.

Ø  R2(config)#router bgp 65001

Ø  Router(config-router)#neighbor 198.51.100.2 route-map ASPATH out

                   This time it gonna be Outbound direction when i am sending Route advertisements to ISP1, i am going to be prepending two additional instances of my own Autonomous System to the ASPATH, let’s do a Soft Reset of BGP again.

Ø  R2#clear ip bgp * soft

                          And let’s go out to the INTERENT Router and see how it looks coming back in the Enterprise Network

                    Notice before, when we looking into the Enterprise network we are going via ISP1 the Autonomous System path had the same length where they went via ISP1 or ISP2, now we should update that such that, it gonna be a longer path to go via ISP1 let’s once again do a

Ø  INET#show ip bgp

                         Look at this now get to this internal 192.0.2.0 network inside of our enterprise network the best Path indicating is with Greater than “>” sign, it’s ISP2 why is that?

                        Well now the Autonomous System Path via ISP2 is significantly Shorter then the path via ISP1 and the reason is, we Prepended a couple of additional instances of our local Autonomous System to the AS Path that was being advertised out the ISP1 and that’s a very real world look at how we could Troubleshoot a scenario where we have a sub-optimal path when an Enterprise network is connecting out to more than 1 ISP remember, we need to influence both Outbound and Inbound Path Selection.

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IPv6 Route Redistribution Considerations

   
                    In this topic, we wanna talk about a couple of additional considerations we have when we were Troubleshooting Route Redistribution for IPv6, for the most part issues are similar but there are couple of additional things i want you to keep in mind beyond what we already talked about.

                       First let’s consider Router running some Routing Protocol, let’s say it’s OSPF and let’s say that Router has several interfaces and those interfaces are participating in OSPF and let’s say, that Router is doing a Route Redistribution of OSPF into another Routing Process with IPv4 the interfaces on that Router that are participating in OSPF they are going to be Redistributed but that’s not the case by default with IPv6, with IPv6 we have to specify an additional parameter to say that we want to Redistribute a connected networks.

                           Now “Route Redistribution works on the premise that, in order to Redistribute a Route into another Routing Protocol, that Route has to exist in the IP Routing Table” and if we take a look in the IP Routing Table if we have an interface on that Router that does participating in OSPF, Yes! the network attach to that interface is going to show up in the Routing Table but not because it was learned via OSPF, it shows up because it’s a directly connected network and if we doing IPv4 Route Redistribution it understands that this interface, it is connected but its participating in the Routing Process so i am going to Redistributed that’s as well.

                          But with IPv6 that does not happen, with IPv6 if i say for example that i want to Redistribute all of my OSPF learned Routes into another Routing Process or all of my EIGRP learned Routes into another Routing Process, those Routes that i am Redistributing not only need to show up in the IP Routing Table because they were learned by OSPF or EIGRP or whatever Routing Protocol is doing a Redistribution.

                         But usually we will want also Redistribute networks connected to interfaces that are participating in that Routing Process and when we go to interface in a movement, i am going to show you the extra parameter, we have to give and here is another difference when we doing Route Redistribution with IPv6 is supposed to IPv4.

                         Remember, with IPv4 when we were Redistributing into OSPF we said that we would normally want to give the “Subnets” option, without the “Subnets” option the only networks that were going to be Redistributed into OSPF, where networks that had there classful mask but now we talking about Redistributing into OSPFv3 which gives us IPv6 support and with IPv6, there is no concept of Subnet or a classful network so, we don’t have to worry about giving the Subnets option and to demonstrate a Mutual Route Redistribution for IPv6

Ø  Between OSPF and EIGRP

Ø  Specifically, OSPFv3 and EIGRP for IPv6.

I already got those Routing Protocols configured on Routes R1, R2 and R3.

Now Let’s configure Route Redistribution, let’s go into Global Configuration Mode

Ø  R2(config)#ipv6 router eigrp 1

Ø  R2(config-rtr)#redistribute ospf 1 1544 10 255 1 1500 include-connected

                  Here we want to give “include-connected” option what i am saying is, i want to Redistribute networks from any interfaces on this Router(R2) that are enabled for OSPF those networks not in the IP Routing Table because they were learned via OSFP, they directly connected networks but we do want to Redistribute those and to make that happen i say “include-connected”.

Now let’s Redistribute EIGRP learned Routes into OSPF

Ø  R2(config)#ipv6 router ospf 1

Ø  R2(config-rtr)#redistribute eigrp 1 include-connected

               There is no Subnets option because IPv6 has no concept of Subnets, i do want to say (include-connected) though just like we did for OSPF Routes that were being Redistributed into EIGRP and we have done.

Let’s go over Router R1 and issue command

Ø  R1#show ipv6 route

               You can see that we have learned couple of networks via Route Redistribution, now let’s go to Router R3 and see what we have learned any OSPF

Ø  R3#show ipv6 route

                    And we do have couple of Routes and that’s the look at couple of differences that we should keep in mind when we doing Route Redistribution with IPv6 as supposed to IPv4 and again there is no Subnets option when we Redistributing with IPv6 and also, we might want to add that (include-connected) option when we doing Redistribution which were cause directly connected networks that are enabled for that Routing Process to also be Redistributed.

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TroubleShooting Route RedistribuTion with Multiple RedistribuTion Points

               If we were designing a network ourselves, we might look at that Redistribution Point and think that’s the potential single Point of failure instead we might want to have 2 or more Routers that are Redistributing between the different Autonomous Systems, different Routing Domains we can certainly do that but in some cases, that might introduce a bit of Troubleshooting issue for example, let say that Router2 on Picture.

                    Wants to send traffic to the 10.1.1.0/24 network and Router R2’s IP Routing Table say’s that the next Hop is Router RD1

                 Which is a Router that’s doing Redistribution, RD1 sends the Packets down to Router R1 and interestingly Router R1 sends the packet on to Router RD2 and Router RD2 sends this packet back into our original Autonomous System

      That could be sub-optimal Routing we leaving our Routing Domain going through another Routing Domain, another Autonomous System and then coming back into our own Routing Domain and you might run into a situation like this

Ø  Depending on how many Domains you have?

Ø  How many boundary Routers you have?

Ø  What specific Routing Protocols you using?

Ø  How things are configured?

In this topic, we want to talk mostly in theory about how we would Troubleshoot an issue like this.

                         What we could do is, set really really high Metric values on a Routes that being Redistributed into a Routing Domain that way if i am in Autonomous System number 2 and i am trying to send packets to a destination that also lives in Autonomous System number 2, i am probably not going to be leaving my Autonomous System because the Metric would be too high to go through another Autonomous System, it would be a much lower Metric to stay with my own Autonomous System something else we might do to combat situation like this, is to statically set the Administrative Distance for a Routing Protocol

     Remember that , RIP has a default Administrative Distance of 120, OSPF has a default Administrative Distance of 110 and EIGRP has default Administrative Distance of 90 except for (external Routes that get injected into EIGRP those have an Administrative Distance of 170) infect since, EIGRP does distinguish between externally learned Routes and Routes leaned within the Autonomous System and it gives a higher Administrative Distance to those externally learned Routes EIGRP by itself does a great job for preventing a situation like this from happing but depending on what Routing Protocol you using and how things configured, you might in some cases need to statically configured the Administrative Distance for Routing Protocol so let’s Hope out to interface and take a look at how easy is to set the Administrative Distance for Routing Protocol.

I am sitting on Router RD1 and its configured for Route Redistribution and if we do a

Ø  RD1#show ip route

                     We have learned Routes via OSPF, we have learned Routes via EIGRP and notice the Administrative Distances of these different Routing Protocols however, in some Troubleshooting scenarios we might want to make OSPF more believable than EIGRP, here how we could do that, we can give the “Distance” command, that command works not just with OSPF, it also works with EIGRP and it works with RIP, here how we can do it

Ø  RD1(config)#router ospf 1

Ø  RD1(config-router)#distance 80

Now if we look at IP Routing Table again

Ø  RD1#show ip route

                        Look at this my OSPF Routes now have a more believable Administrative Distance then EIGRP, it’s now AD of 80 and you can see that we don’t have any EIGRP learned Routes in the IP Routing Table now because i have learned all of them via OSPF.

                         But something important to realize is that this Administrative Distance of 80 is only locally significant, it only applies to Router RD1 Route configured it, another words this Administrative Distance is not being advertised out to other Routers this is not going to influence the Routing decision that other Routers make, this only influences RD1

                        Another fairly clever way to overcome this Routing Loop issue is to “Tag a Route” as its being Redistributed from one Routing Domain into another and when we talk about Tags, please realize we can use this for lots of different reason not just for Redistribution but what is a Tag?

                      It’s a value that we can assign to a Route and Tag isn’t a really measuring anything it’s not a specific unit of measure for bandwidth or delay or anything like that it’s just a Label that we put on a Route let’s checkout an example, what we can do with Tags.

                         What we could is say that, we want to assign a Tag of 10 to Routes being Redistributed into Autonomous System 1 on picture.

            And i have just drown for Router RD1 but we would do the same thing for router RD2 but in addition to setting the Tag to 10 for Routes going into Autonomous System 1. What if we did this also, what if we said that we going to deny any Routes from being Redistributed that had a Tag of 10 in the example of picture.

                  We got a Route going from Autonomous System 2 into Autonomous System 1 but as that Route gets Redistributed it’s given a Tag of 10 and RD1 in the example, is assigning that Tag if that’s same Route were to then try to comeback into Autonomous System 2 via RD2 that’s not going to be allowed because RD2 is gonna have a Route-Map that says we are not going to allow the Redistribution of any Route that has a Tag of 10 going into Autonomous System 2.

Let’s go out an interface now and take a look at how we can configure these Tags

                       We here again on Router RD1 and what we want to do is to say if we were Redistributing our Route from EIGRP into OSPF we want to give it a Label we gonna give it a Tag of 10 and we can do that with Route-Map, let’s do that

Ø  RD1(config)#route-map TAG10

Ø  RD1(config-route-map)#set tag 10

ü  TAG10: Route-Map Name

ü  10: Tag Number

Let’s create a second Route Map

Ø  RD1(config)#route-map DENYTAG10 deny 10

ü  DENYTAG10: Route-Map Name

ü  deny: Deny Statement

ü  10: Sequence Number

What I am wanting to deny, i am wanting to deny Routes that have a Tag of 10

Ø  RD1(config-route-map)#match tag 10

                      We gonna deny that being Redistributed from OSPF back into EIGRP thus breaking that potential Routing loop however, i want to allow other traffic to be Redistributed, i need to allow everything else so, we need to give a second Route-Map statement for the deny tag 10

Ø  RD1(config)#route-map DENYTAG10 permit 20

ü  DENYTAG10: Previous Route-Map Name

ü  Permit: Permit everything

ü  20: higher Sequence Number because (10 Sequence number is denying)

                    Now need to match anything because the default is going to match everything now the we got those Route-Map created, let’s apply them to our Routing Process.

Ø  RD1(config)#route ospf 1

Ø  RD1(config-route-map)#redistribute eigrp 1 subnet route-map TAG10

                          I am assigning Tag of 10 to Routes being Redistributed into OSPF from EIGRP, now let’s apply the other Route-Map to the EIGRP Routing Process.

Ø  RD1(config)#router eigrp 1

Ø  RD1(config-route-map)#redistribute ospf 1 route-map DENYTAG10

I have already set the Default Metric

                   I am saying if i am Redistributed into EIGRP from OSPF, i am going to deny any Routes that have a Tag of 10 and in this example, i did this two one of my Redistribution point RD1, to complete the Configuration i would need to do the same thing on Router RD2 which is my other Redistribution Point.

   That’s the look at a few different ways that we can Troubleshoot a Routing Loop that might occurred when where doing Mutual Route Redistribution between a couple of different Routing Domains and we have more than 1 Redistribution Point.

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Review of Route Redistribution

  

                            We learned about the concept of Route Redistribution back in the Route Complete Course and we said that Route Redistribution allows routes that learned from one Routing Source

Ø  Maybe like Routing Protocol

Ø  Maybe a directly connected Routes

Ø  Maybe a Statically configured Route

But we learned Routes from some source and those Routes can be injected into a specific Routing Protocol for example, we could Redistribution Routes from OSPF into EIGRP and before we get into Troubleshooting Route Redistribution, let’s take a few movements and review the basics.

First why would we want to do Route Redistribution?

Ø  Well one reason we might want to do Route Redistribution is we got an enterprise network and its running more than one Interior Gateway Protocol

Ø  Maybe because there is a company merger, Company A merge with Company B and one was running OSPF and other was running RIPv2, we might need to Redistribute between those 2 different Interior Gateway Protocols

Ø  Maybe we got different departments within the enterprise that are under different Administrative Control or perhaps we got a Partner Company, it’s not our Enterprise but it’s a Company we do a lot of work with maybe we want to connect out to those partner networks

Ø  We don’t have to do Route Redistribution just between Interior Gateway Protocols, we could Redistribute between an Interior Gateway Protocol and an Exterior Gateway Protocol specifically BGP Border Gateway Protocol

Ø  Maybe we want to advertise our Routes out of Server Provider and we got a BGP Peering Relationship with that Service Provider

Ø  Maybe the reverse we want to take BGP learned Routes and Redistribute those or maybe a subset of those into our IGP

                   As an example, let’s think about this Router it’s got one interface in one Autonomous System and another interface in that different Autonomous System the interface is on the left is connected into EIGRP Autonomous System and interface on the right side connected into OSPF Autonomous System

                              What we can do is take Routes known to EIGRP and inject those into OSPF, similarly we can take Routes known to OSPF and inject those into EIGRP that would be an example of “Mutual Route Redistribution”

                        That’s where we got a couple of different Routing Protocols and each Routing Protocol is sending its Routes into the other Routing Protocol and when we configure Route Redistribution, here is key point to keep in mind often time it can get confusing in which direction the Redistribution is happening.

                      If i go into Router EIGRP 100 Configuration Mode, i am in the Router Configuration for an EIGRP Autonomous System and i give the Redistribute command under EIGRP Router Configuration Mode what i am saying, am i saying that i want to take EIGRP learned Routes and Redistribute them somewhere else.

                     No! What i am saying with Redistribute command is “Redistribute Routes from the specified Routing Source their we gonna specifying in Redistribution command, redistribute those into this Routing Protocol” in my case, i am in EIGRP Router Configuration Mode.

                   I say Redistribute, maybe i am redistributing OSPF, i am Redistributing those OSPF Routes into EIGRP, when i say that i want to Redistribute routes learned by a specific Routing Protocols it’s not just Routes learned by that Protocol, it also includes Routes to networks on directly connected interfaces and those interfaces are enabled for this Routing Protocol those will be Redistributed as well

                  One of the big challenges we have with Redistribution is Routing Protocol use different metrics they got different criteria for what makes up a metric

Ø  OSPF’s metric is based on Cost(Bandwidth).

Ø  And by default, EIGRP’s metric based on Bandwidth and Delay, even though it can consider other things depending on our K Values.

Ø  RIP its metric is based on Hop Count, how many Routers do we have to transit in order to get to this network.

And it really doesn’t make any sense to try to do something like this, we could not say for example, if an OSPF Routes has a metric of 10 and we were Redistributing it into RIPv2 then give it a Hop Count of 3, it really doesn’t make sense to do something like that because these Routing Protocols are calculating their metrics very very differently so, what we can do. There are some default Seed metric

                   “A Seed Metric can be assigned by default to our Route as its being Redistributed into a Routing Protocol” that’s if we don’t manually configure a metric ourselves which we can do, and different Routing Protocol have different Seed Metric and i want you to understand what’s those are, lets populates the Table to see what default Seed Metric are for various Routing Protocols

Ø  The default Seed Metric for RIP is Infinity, if we Redistribute a Route into RIP by default RIP is gonna consider that Route Unreachable

Ø  The default Seed Metric for EIGRP also Infinity

Ø  However, its’ bit different with OSPF, with OSPF if we Redistribute the Route into OSFP that Route is going to inherit a default Seed Metric of 20 unless we Redistributing from BGP that’s an exception if the Route is being Redistributed from BGP, in that case it’s gonna have an OSPF metric of 1

Ø  And BGP is an interesting one, its gonna use whatever the IGP Metric value is as the default Seed Metric.

Now the we reviewed some of the fundamentals of Route Redistribution

Ø  We discussed why we need it?

Ø  What does it do?

Ø  What are the defaults Seed Metric?

                     Let’s go to interface and review a Basic Route Redistribution Configuration and then in our next session we get into Troubleshooting Route Redistribution. Here in Router R2

       We gonna configure the Route Redistribution because it’s the boundary Router it’s got an interface in the OSPF Autonomous System and it’s got another interface in EIGRP Autonomous System this is the place we gonna set things up, let’s see what the Router Configuration looks like right now in R2

Ø  R2#show run | s router

             And we see that for EIGRP interface serial 1/1, if we look at the topology is participating in EIGRP and the OSPF Autonomous System includes our loopback 0 interface as well as serial 1/0. Now let’s set up Mutual Router Redistribution let’s start by Redistributing OSPF learned Router into EIGRP

Ø  R2(config)#router eigrp 1                 

Ø  R2(config-router)#redistribute ospf 1

Now i am gonna setup default metric which will apply to all routes being redistributed into EIGRP

Ø  R2(config-router)#default-metric 1554 10 255 1 1500

ü  1554: Bandwidth (Kbps)

ü  10: Delay (Microseconds)

ü  255: Reliability

ü  1: Load

ü  1500: MTU (Bytes)

                                               Remember the metric for EIGRP is made up of “bandwidth, delay Reliability, Load and MTU (where MTU is not really used in calculation)” but its designed to be Tie-Breaker and by default only Bandwidth and Delay is considered but we can manipulate the K Values to make “Load and Reliability” also be considered here.

                      Once we done that, we should now be Redistributing OSPF known Routes into EIGRP, let’s see if that True, let’s go to R3 and see if we learned anything

Ø  R3#show ip route

                       We have learned about the Loopback IP Address on R1, the Loopback IP Address on R2 we have learned about the network connected of fastetherent 0/0 on R1 and we have learned about network interconnecting R1 and R2, Great News! However, just because R3 knows about these networks how to get to those networks, that’s no guarantee that we can setup conversation with a host on one of those networks for example, let’s try a ping

Ø  R3#ping 1.1.1.1

                     It’s in the IP Routing Table but the ping is gonna failed what do they fail? i am getting to 1.1.1.1 however, that Router R1 it does not know how get back to me and as result all of the Pings failed. We have only Redistributed in one direction, we have Redistributed OSPF into EIGRP let’s go to other direction now, let’s go to R2

Ø  R2(config)#router ospf 1

Ø  R2(config-router)# Redistribute eigrp 1

                      I could say that i wanted to specify a metric in this point but remember OSPF does have a default metric it going to assign to Redistributed Routes, it’s gonna be a metric of 20 unless that Redistributed Routes is coming from BGP in that case metric is gonna be 1 but here i am just gonna leave it at default of 20.

                         Something that we typically want to do is include the “Subnets” keyword, the “Subnets” keyword cause us to Redistribute all ospf knows Routes into EIGRP, if we do not give the “Subnets” keyword we only gonna be Redistributing classful networks infect it get show us warning that “only Classful network are going to be Redistributed”, let’s prove that

Let’s take a look at our OSPF database

Ø  R2#show ip ospf database

                    I am looking for Type 5 LSA’s, a Type 5 LSA would represent a network that we learned another Autonomous System and I don’t see any right now. Just as experiment, let’s create another network in R3 in the EIGRP Autonomous System that does have a classful subnet mask, i am going to R3 and just as a test let’s create Loopback1

Ø  R3(config)#interface loopback 1

And i am assigning Classful Subnet Mask

Ø  R3(config-if)#ip address 4.4.4.4 255.0.0.0

                  This is just an experiment now see let’s that network that classful network, did it get Redistributed into the OSPF, let’s go back to R2

Ø  R2#show ip ospf database

                 Look at this we got Type 5 LSA representing that Classful network, so this point we will Redistributed in Classful networks but we don’t have any other network that have a classful mask, how do we fix that let’s go back to Router 2

Ø  R2(config)#router ospf 1

Ø  R2(config-router)# Redistribute eigrp 1 subnets

Once i do that let’s take a look at OSPF database

Ø  R2#show ip ospf database

                    Great News! We have plenty of Type 5 LSA’s now we know about all of these networks at this point all three should be able to ping the Loopback interface on Router R1

Ø  R3#ping 1.1.1.1

Let’s go to R1

Ø  R1#show ip route

                          And the E2 Codes tells us these are the networks learned them an external Autonomous System

                         E2 is the default as we saw on R1 but the difference between E1 and E2 is “when a Route is being Redistributed as E2 or Type 2 External Route then it’s metric is gonna remain as the same” it’s gonna be the metric assigned by the ASBR, by the Autonomous System Boundary Router regardless of how many router Hop’s it has to go through within an OSPF Areas it still gonna have that original metric assigned by the ASBR, if i am 3 Router Hop’s away and i say what’s the metric to get back this network, it’s gonna be the same metric as the ASBR reported.

You might think that’s not terribly accurate, i want to consider the cost to get from this router back to the ASBR, If you want to consider the metric to get from a router to the ASBR and add that Cost on to the Cost Advertised by the ASBR that’s where you need to set the metric-type to 1(E1)

Ø  (config-router)#redistribute eigrp 1 subnets metric-type 1

That would be an E1 instead of the E2 that we have by default and E1 route it will consider the distance to get to the ASBR and then add on to that Distance of Cost to get to the Destination network

And now the we reviewed the basic Route Redistribution Configuration, let’s take a look at our next session at Trouble Ticket.

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