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Statict routes Redistributed in EIGRP

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
Bronze

Statict routes Redistributed in EIGRP

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

Cisco Employee

Statict routes Redistributed in EIGRP

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

24 REPLIES
Cisco Employee

Statict routes Redistributed in EIGRP

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

New Member

Statict routes Redistributed in EIGRP

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

Bronze

Statict routes Redistributed in EIGRP

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

Cisco Employee

Statict routes Redistributed in EIGRP

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

Bronze

Statict routes Redistributed in EIGRP

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

Cisco Employee

Statict routes Redistributed in EIGRP

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

New Member

Statict routes Redistributed in EIGRP

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

Cisco Employee

Statict routes Redistributed in EIGRP

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

New Member

Statict routes Redistributed in EIGRP

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

Cisco Employee

Statict routes Redistributed in EIGRP

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

New Member

Statict routes Redistributed in EIGRP

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

Cisco Employee

Statict routes Redistributed in EIGRP

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

New Member

Statict routes Redistributed in EIGRP

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

Cisco Employee

Statict routes Redistributed in EIGRP

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

New Member

Statict routes Redistributed in EIGRP

Hi Peter,

Many thanks for explaining me in great detail.

Sorry for causing confusion to eveyone.

I will spent some time in going through your replies and  studying  more about EIGRP redistribution before i ask

further questions

Best regards

MAhesh

VIP Super Bronze

Statict routes Redistributed in EIGRP

Hi Mahesh,

In addition to explanation by Peter. Looking at the config in your post, you have this command:

no passive-interface Serial0/0

That means interface s0/0 is part of EIGRP network and that is why you see 192.168.50.x in the EIGRP topology.

Or did I misundestand your question?

Reza

Cisco Employee

Statict routes Redistributed in EIGRP

Hi Reza,

That means interface s0/0 is part of EIGRP network and that is why you see 192.168.50.x in the EIGRP topology.

Hmmm... Mahesh said that there is no network 192.168.50.0 command configured on either of his routers which makes me suspicious about what's going on. To my best knowledge, setting the S0/0 interface as "no passive" without specifying it via a network command is not sufficient to have it advertised.

Best regards,

Peter

VIP Super Bronze

Statict routes Redistributed in EIGRP

Hi Peter,

So, than what is the purpose of this command under EIGRP process?

Mahesh,

Can you post "sh run" from both routers?

Thanks,

Reza

Cisco Employee

Statict routes Redistributed in EIGRP

Hi Reza,

So, than what is the purpose of this command under EIGRP process?

The snippets of Mahesh's configuration show that he has passive-interface default and no passive-interface S0/0 configured, thereby allowing EIGRP communication only via S0/0 interface even if other interfaces are included into EIGRP using appropriate network commands.

Having an interface declared as passive or "non-passive" does not automatically mean that it is going to be advertised by EIGRP. An interface must first be included into EIGRP by a network command to be advertised. Configuring it as passive merely prevents EIGRP from sending and receiving EIGRP packets over it - if and only if it is covered by a network command. If an interface is not covered by a network command, declaring it explicitly as passive or "non-passive" has no effect.

There is an exception to this rule: In IS-IS, declaring an interface passive will automatically cause it to be advertised (as if you configured the ip router isis on this interface) but prevents IS-IS from forming adjacencies over that interface. The same is valid if running EIGRP for IPv6.

I am not sure if I answered your question - please do ask further.

Best regards,

Peter

VIP Super Bronze

Statict routes Redistributed in EIGRP

Hi Peter,

Thanks for the excellent explanation.  I thought, the purpose of this command was that you did not have to explicitly add the network command since you add the physical or logical interface to the process, but apparently my thought was wrong.   Just adding the interface is not enough, you still have to apply the network command, which seems to be redundant.  To me, it would make sense to just add the network command or the interface.  Maybe I am looking at this, because of the way other vender's deploy protocols.  For example, on a Juniper router, you create the process and add the physical or logical interface to it.  You don't need any network command.  I thought, Cisco is going down the same path.

Best Regards,

Reza

Cisco Employee

Statict routes Redistributed in EIGRP

Hello Reza,

I thought, the purpose of this command was that you did not have to  explicitly add the network command since you add the physical or logical  interface to the process

That's the gotcha Cisco's legacy style of configuring routing protocols is to add interfaces using the network command only. Declaring an interface as passive/non-passive is only an additional tweaking of the protocol's operation on an interface once it has been added via the network command, but it is not considered as adding the interface to the routing protocol per se. Needless to say, it is strongly confusing.

The IS-IS has been the only routing protocol in IOS that, to my best knowledge, never used the network command and instead added interfaces directly. Since IOS 12.3, also OSPF can be configured directly on an interface using the command ip ospf area. Things are different with IPv6 routing protocols: neither of them uses the network command and all are configured directly on interfaces.

Just adding the interface is not enough, you still have to apply the network command, which seems to be redundant.

Exactly. But as I indicated - declaring the interface as passive/non-passive is not considered as adding the interface to the routing protocol (save IS-IS and EIGRP for IPv6).

For example, on a Juniper router, you create the process and add the  physical or logical interface to it.  You don't need any network  command.  I thought, Cisco is going down the same path. 

With IS-IS, it has always been this way. OSPFv2 supports this approach since IOS 12.3. Other IPv4 routing protocols have only the network command available. IPv6 protocols are a different beast here... fortunately

Best regards,

Peter

VIP Super Bronze

Statict routes Redistributed in EIGRP

Hi Peter,

Thank you so much for clarification. I guess Cisco does a good job of keeping as confused by deploying one protocol one way and another protocol in a different way.  I always ask our SEs the question of why can it all be done the same way?

If other venders can do it, Cisco can certailly do the same.  And the answer is, we are moving that way with IOS XE, Nexus -OS, etc.... hmmm

So, the conclusion is that this command under the EIGRP process is not necessary, since the network command does the job anyway.

Thanks again

Reza

New Member

Statict routes Redistributed in EIGRP

Hi Reza,

Do you still need config of Routers ?

LEt me know

thanks

MAhesh

VIP Super Bronze

Statict routes Redistributed in EIGRP

Mahesh,

No need.  It is clear now.

Thanks,

Reza

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