default gateway lost in routing table.

[FOROOZAN BANIFATEMI]

Hi all,

does anyone know why a 3550 or 3560E (working as a router), would lose its default gateway (0.0.0.0) in ip route? my router lost the default gateway after the following two log errors. the only way to fix the issue was to clear the ip route to bring the default gateway back into routing table.

IOS  Version 12.2(52)SE 

19:00:44.836: %SYS-5-RESTART: System restarted --

19:00:45.212: %PIM-5-DRCHG: DR change from neighbor 0.0.0.0 to 1.1.1.1 on interface Loopback0

19:00:46.212: %PIM-5-DRCHG: DR change from neighbor 0.0.0.0 to 10.70.32.1 on interface Vlan10

Thanks for your help in advance.

FB

[Jon Marshall]

FB

Can you clarify -

a device working as a router does not need a default-gateway, it needs a default-route ie.

ip default-gateway x.x.x.x  <-- this is when the switch is acting as L2 device

ip route 0.0.0.0 0.0.0.0     <--- this is used when the device is acting as a router

if it is a default-route, is this statically configured on your switch or do you receive it from another L3 device via a routing protocol ?

Jon

[FOROOZAN BANIFATEMI]

Thank you Jon.

my mistake! it is a dafualt route and is assigned dynamically by the EIGRP.

[Jon Marshall]

When you lost the route did you lose any other routes ?

The router that you receive the default-route from via EIGRP, did the EIGRP neighborship stay up ?

Jon

[FOROOZAN BANIFATEMI]

yes everything else is up. onlt route to 0.0.0.0 was lost so acccess to the Internet.

[Jon Marshall]

The PIM DR log messages are not error messages, they are informational. From the looks of the log your switch restarted itself and these are just messages you would normally see as the switch sorts out it's PIM DRs.

Are you sure the switch didn't restart ?

Jon

[Reza Sharifi]

FB,

In addition to Jon's comment, can you check to see if there is any crash file info written in the flash?

Did this happen only once?

Reza

[FOROOZAN BANIFATEMI]

Thank you all for your comments. just to clarify, we have many remote sites (with our own router onsite) that connect to our core router through provider's WAN (eigrp) and then traffic for the Internet is forwarded to the firewall from the core router. I got some complaints about problem accessing the Internet from different sites. when I checked the router in one of the sites, I found that the default route was gone. however everything else was working fine. after clearing ip route the default route came back to ip route and users were ok then. I applied the same solution to all affected routers. Today I just found that they all had been restarted before taking that hit.

I also chekd the flash and there was no crash dump in there as follow:

    4  -rwx        2072  Feb 28 1993 19:00:50 -05:00  multiple-fs

    5  -rwx          47   Jun 6 2010 15:26:11 -04:00  system_env_vars

    6  -rwx         676  Feb 28 1993 19:00:44 -05:00  vlan.dat

    7  -rwx        9003  Feb 28 1993 19:00:49 -05:00  config.text

    8  -rwx          15   Jun 6 2010 15:26:11 -04:00  env_vars

    9  -rwx          24  Feb 28 1993 19:00:49 -05:00  private-config.text

I have already left the office and won't be back until next Thursday, becasue of a training course. therefore I will have to check your comments less frequently.

Thank you again.

FB

[dslice]

Where is the default route originated and how is it created? It might be be redistributed static or summary route or possibly redistributed from another protocol. Did it disappear from the source or somewhere downstream? Were all receivers of the default missing it or just some?

[FOROOZAN BANIFATEMI]

just as an FYI item, following is the response from the Cisco TAC:

The problem you are seeing is very similar to the following software defect that affects your current IOS versions:

CSCte69761   

Default Route deleted when prefix marked as candidate default is deleted

Externally found moderate (Sev3) bug: R-Resolved

This is an external defect you can access on Cisco.com. The fix for this issue is available in the following IOS versions and higher:

12.2(55)SE

12.2(54)SG

12.2(53)SG3

12.2(53)SE1

12.2(50)SG8

This defect was originally triggered when there were multiple candidate default routes in the routing table (a default network received from another EIGRP device and the 0.0.0.0/0 prefix).  When the default network is removed this also causes the 0.0.0.0 route to be removed.  The only way to clear the issue is to clear the route.  At the time the output was collected from Lescon-35-1 there was not a second candidate default in the routing table.  It is possible that either (1) when the problem occurs we are receiving and deleting a default network or (2) there is another underlying trigger for this defect.  We have seen other customers hit this problem without the specific default network noted above.