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Statict routes Redistributed in EIGRP

mahesh18
Level 6
Level 6

Hi,

I was reading this statement

EIGRP does not add static routes to the EIGRP topology table unless that routes are

redistributed.

Say Router A  has direct connection to Router B.

And Router A   fa int IP is 192.168.50.2

Router B  has int IP  192.168.50.3

So this mean that if router A  has default route  like 0.0.0.0 0.0.0.0.0 192.168.50.3

and if i do the sh ip eigrp  topology on the router A

it still shows route to

192.168.50.0 subnet?

Can someone please explain me why this happened?

thanks

mahesh

2 Accepted Solutions

Accepted Solutions

I may not be understanding fully either -- but you are asking if Router A will still show static default route in its routing table without the static redistribute command?  The answer here would be Yes.  Your routing table would show a static default route, any directly connected routes, and in addition any other routes learned from EIGRP.

With regard to why you are seeing the 192.168.50.2/31 route in Router A's EIGRP topology when you don't have the network statement in Router A's EIGRP configuration, is there a network statement that would match this network in the other directly-connected router (aka Router B)?

Matt

View solution in original post

Hi Mahesh,

So as per above we can say that Router A  shows the default route right???????????

Yes. Now the default route is being injected into EIGRP from another router and advertised to Router A.

IT is inaccessible because  it has higher Admin dustance then connected router right?

Not entirely. It is inaccessible because it has a higher administrative distance than the static default route already present in your routing table in this case.

By both routes i mean 192.168.50.0.

The "192.168.50.0/31" is just a heading - a title - in the printout, not a real network. There is really only one 192.168.50.x network in your routing table - the 192.168.50.2/31. The title "192.168.50.0/31" means that all subnets of the once-classful network 192.168.50.0 are having the netmask of /31 and are listed below the title. Once again, the "192.168.50.0/31" in your routing table is not a network.

Best regards,

Peter

View solution in original post

24 Replies 24

Peter Paluch
Cisco Employee
Cisco Employee

Hi Mahesh,

I am not sure if I understand what you find surprising in the EIGRP behavior. The 192.168.50.0 subnet should be present in your EIGRP topology because it is a directly connected network on router A that has been included into EIGRP using the network command. However, the static default route will not be in the EIGRP's topology table unless you use the redistribute static command.

Perhaps you could try to explain the issue in different words.

Best regards,

Peter

Hi Peter,

Thanks for reply.

192.168.50.x subnet has not been included in network eigrp command using Router A.

Here is config on A  router

router eigrp 90

passive-interface default

no passive-interface Serial0/0

network 10.1.0.0 0.0.255.255

network 15.15.15.15 0.0.0.0

network 172.30.0.0

no auto-summary

ip route 0.0.0.0 0.0.0.0 192.168.50.3

sh ip eigrp topology shows

P 192.168.50.2/31, 0 successors, FD is Inaccessible**********************************

        via 10.1.24.2 (26137600/25625600), Serial0/0 P 192.168.50.2/31, 0 successors, FD is Inaccessible
        via 10.1.24.2 (26137600/25625600), Serial0/0

I have to static redistribute command on the Router A  still it shows static default route on Router A?

is this normal behaviour?

thanks

mahesh

I may not be understanding fully either -- but you are asking if Router A will still show static default route in its routing table without the static redistribute command?  The answer here would be Yes.  Your routing table would show a static default route, any directly connected routes, and in addition any other routes learned from EIGRP.

With regard to why you are seeing the 192.168.50.2/31 route in Router A's EIGRP topology when you don't have the network statement in Router A's EIGRP configuration, is there a network statement that would match this network in the other directly-connected router (aka Router B)?

Matt

Hi Mahesh,

I have to static redistribute command on the Router A  still it shows static default route on Router A?

is this normal behaviour?

Yes, that is normal. Even if routes are redistributed into a different routing protocol, their original protocol does not change in your routing table. It would not work otherwise - just imagine that your static default route would change to an EIGRP route after redistribution. That would mean that the redistribute static command no longer applies to it because it is not static anymore - and it would fall out from EIGRP, becoming static again, and the entire cycle repeating all over again.

This is a common misunderstanding with redistributed routes. Remember: on the router performing redistribution, the source protocol of redistributed routes does not change.

Regarding the network 192.168.50.2/31, if Router A does not include it into EIGRP using the network command then I assume that Router B does. Am I correct in this assumption?

Best regards,

Peter

Well said Peter - stated more clearly than mine I think!

Hello Matt,

Thank you very much! I am glad you joined the thread. And it is nice to see how similarly we both think

Best regards,

Peter

Hi Peter,

Thanks for reply.

I check the Router B  it also has no network command 192.168.50.0 Router EIGRP config.

Correction below for last post--in bold -  no----

I have no static redistribute command on the Router A  still it shows static default route on Router As Eigrp topology

table.is this normal behaviour?

So my understanding  is that for above statement to be true its ok to have

192.168.50.2 in EIGRP topology table without redistribute eigrp static command?

mahesh

Mahesh,

There are too many unclear things about how exactly are your routers interconnected and how they are configured. Please be so kind to post the full configuration of both routers and if possible, draw a quick sketch of your network - or at least include the show cdp neighbors output from both routers. Thank you!

Best regards,

Peter

Hi Peter,

Thanks for reply.

Seems i have found the issue

Router A  connects to Router B

Also Router A  has EIGRP connection to Router C.

Router A = BB

BB#sh cdp nei
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
3550SMIA.manveer.com
                 Fas 0/0            150        R S I      WS-C3550- Fas 0/13
2650XM           Ser 0/0            142        R S I      2650XM    Ser 0/1

Router B ===3550SMIA

3550SMIA#sh cdp nei
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
BB               Fas 0/13          144          R S I     2650      Fas 0/0
2650XM           Fas 0/4           144          R S I     2650XM    Fas 0/0
3550SMIB         Gig 0/1           132          R S I     WS-C3550- Gig 0/1
3550SMIB         Gig 0/2           132          R S I     WS-C3550- Gig 0/2
2691Router
                 Fas 0/11          135          R S I     2691      Fas 0/1
2650Router       Fas 0/1           162           R S      2650      Fas 0/0

Router C  =====2650XM

2650XM#sh cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
BB               Ser 0/1            120        R S I      2650      Ser 0/0
3550SMIA.manveer.com
                 Fas 0/0            174        R S I      WS-C3550- Fas 0/4
2620Router       Fas 1/0            122          R        2620      Fas 1/0
2620Router       Ser 0/0            148          R        2620      Ser 0/0

Router C is doing redistribution of EIGRP into OSPF and OSPF into EIGRP

Router C  config

router eigrp 90

redistribute ospf 1 metric 100 100 100 100 100**********************************************

When i remove the above redistribute command from Router C  then on Router A  if i do

sh ip eigrp topology

sh ip eigrp topology
IP-EIGRP Topology Table for AS(90)/ID(172.30.8.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 15.0.0.0/8, 1 successors, FD is 281600
        via Connected, Ethernet1/0
P 10.1.24.0/30, 1 successors, FD is 2178560
        via Connected, Serial0/0
P 172.30.2.0/24, 1 successors, FD is 128256
        via Connected, Loopback2
P 172.30.3.0/24, 1 successors, FD is 128256
        via Connected, Loopback3
P 172.30.0.0/24, 1 successors, FD is 128256
        via Connected, Loopback0
P 172.30.1.0/24, 1 successors, FD is 128256
        via Connected, Loopback1
P 172.30.6.0/24, 1 successors, FD is 128256
        via Connected, Loopback6
P 172.30.7.0/24, 1 successors, FD is 128256
        via Connected, Loopback7
P 172.30.4.0/24, 1 successors, FD is 128256
        via Connected, Loopback4

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 172.30.5.0/24, 1 successors, FD is 128256
        via Connected, Loopback5
P 172.30.8.0/24, 1 successors, FD is 128256
        via Connected, Loopback8

As above now it does not show static default route of 192.168.50.2.

When i put the redistribute osp 1 command back on router C

Router A  shows

P 192.168.50.2/31, 0 successors, FD is Inaccessible

        via 10.1.24.2 (26137600/25625600), Serial0/0 P 192.168.50.2/31, 0 successors, FD is Inaccessible
        via 10.1.24.2 (26137600/25625600), Serial0/0

Does it make sense peter?

Also it shows that while  redistributing into EIGRP  even if we do not put command

redistribute eigrp static  then also it shows static  default route in eigrp topology table of  router A  correct?

thanks

mahesh

Hello Mahesh,

The information from you are still very partial and they do not give us a good overview of how your network looks like, where do the individual routing protocols run and how are individual routers configured. I am only doing my best guess here.

As above now it does not show static default route of 192.168.50.2.

But that is not a "static default route" at all, my friend. A static default route must be a network 0.0.0.0/0. No other network can be called a default route. The 192.168.50.2 may theoretically be a next hop towards the default route but never a default route itself.

Now, what you see here when activating and deactivating the redistribution from OSPF to EIGRP is relatively simple. OSPF somehow knows about the network 192.168.50.2/31. When you redistribute from OSPF to EIGRP, information about this network is injected into EIGRP and is propagated to router A. However, when router A's EIGRP tries to enter this network into the routing table, it find out that the network 192.168.50.2/31 is already present in the routing table as a directly connected route. Because the directly connected route 192.168.50.2/31 has the administrative distance of 0, it is considered more trustworthy than the EIGRP-learned external network with administrative distance of 170. That is the reason why the 192.168.50.2/31 is present in your topology table marked as Inaccessible.

Best regards,

Peter

Hi Peter,

thanks for reply again.

On Router A  i have this config

ip route 0.0.0.0 0.0.0.0 192.168.50.3  so this is not static default route?

And 192.168.50.2 is next hop towards default route

Also from Router A

sh ip route shows

Gateway of last resort is 192.168.50.3 to network 0.0.0.0

S*   0.0.0.0/0 [1/0] via 192.168.50.3

BB#

D EX    192.168.6.2 [170/26137600] via 10.1.24.2, 00:55:10, Serial0/0

     192.168.50.0/31 is subnetted, 1 subnets

C       192.168.50.2 is directly connected, FastEthernet0/0

Also Router A  shows both the routes learned for 192.168.50.0

But you are absoutley correct as admin distance of directly connected is lower thats why it shows 192.168.50.2

in the topology table

Thanks

MAhesh

Hello Mahesh,

On Router A  i have this config

ip route 0.0.0.0 0.0.0.0 192.168.50.3  so this is not static default route?

Yes, that is a static default route. However, in your show ip eigrp topology outputs, you have always pointed out the 192.168.50.2/31 network and called that a "static default route" which it isn't. Also note that the default route 0.0.0.0/0 never showed up in any of your show ip eigrp topology listings. That was quite confusing, as I was looking for the network 0.0.0.0/0 while you were only speaking about the network 192.168.50.2/31. That the IP address 192.168.50.3 happens to be the next hop towards the default route on Router A is largely unimportant.

And 192.168.50.2 is next hop towards default route

No, it is not. The next hop is, according both to the ip route command and the show ip route output, 192.168.50.3.

sh ip route shows

Gateway of last resort is 192.168.50.3 to network 0.0.0.0

S*   0.0.0.0/0 [1/0] via 192.168.50.3

BB#

D EX    192.168.6.2 [170/26137600] via 10.1.24.2, 00:55:10, Serial0/0

     192.168.50.0/31 is subnetted, 1 subnets

C       192.168.50.2 is directly connected, FastEthernet0/0

Also Router A  shows both the routes learned for 192.168.50.0

I apologize but which "both" routes do you mean here?

Best regards,

Peter

Hi Peter,

Sorry for the confusion

Router A

BB#sh ip eigrp topology
IP-EIGRP Topology Table for AS(90)/ID(172.30.8.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 0.0.0.0/0, 0 successors, FD is Inaccessible, tag is 1*************************************
        via 10.1.24.2 (26137600/25625600), Serial0/0

So as per above we can say that Router A  shows the default route right???????????

IT is inaccessible because  it has higher Admin dustance then connected router right?

By both routes i mean 192.168.50.0.

Thanks

MAhesh

Hi Mahesh,

So as per above we can say that Router A  shows the default route right???????????

Yes. Now the default route is being injected into EIGRP from another router and advertised to Router A.

IT is inaccessible because  it has higher Admin dustance then connected router right?

Not entirely. It is inaccessible because it has a higher administrative distance than the static default route already present in your routing table in this case.

By both routes i mean 192.168.50.0.

The "192.168.50.0/31" is just a heading - a title - in the printout, not a real network. There is really only one 192.168.50.x network in your routing table - the 192.168.50.2/31. The title "192.168.50.0/31" means that all subnets of the once-classful network 192.168.50.0 are having the netmask of /31 and are listed below the title. Once again, the "192.168.50.0/31" in your routing table is not a network.

Best regards,

Peter

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