Certain ranges not following default route on 6509

[nmjones]

Hi, hopefully someone can help

I have a 6509 with IOS version 12.2(18)SXF14.

I am using a subnetted 10.0.0.0 range, some of the subnets have been learnt via external EIGRP and the rest will be found via an edge router that is the default route for the 6509.

My problem is that the routes learnt via EIRGRP work fine but the other addrsses that don't appear in the routing table should in my mind forward to the default router and then onto the correct destination next hop. Pings fail and a traceroute doesn't  show any results just *'s.

I have added a static route for one of the addresses and pointed it's next hop to be the same as the default route, this now works fine!

Can anyone shed any light on why these addresses don't follow the normal default route statement?

Thanks in advance

Nick

[lgijssel]

Check if have configured classless routing.

For the behavior you want:

ip classless

Probably now configured:

no ip classless

Some background info on the subject:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094823.shtml#classless

regards,

Leo

[Peter Paluch]

Hi Leo,

Very good point, but hmmm... That coud indeed be the case if the router in question was a software router. However, the 6500 is a multilayer switch, and as far as I know, you cannot deactivate CEF on these platforms, and the no ip classless has effect only if the CEF is deactivated. Is it actually possible on 6500 Catalyst series to see classful routing in action?

Best regards,

Peter

[jeffjadryev]

Hi Nick,

Are the destination IP ranges that are not using the default route in 10.0.0.0/8? I think it's possible that auto-summarization might be configured and be the cause of the problem but need more information.

What does the output of "show ip route" for one of the problem addresses look like? Could you post the EIGRP portion of the 6509's configuration?

Thanks,

- Jeff

[nmjones]

Firstly thank you for the responses

The command "IP Classless" is present in the config unfortunately. Below is the EIGRP config from the switch and the relevant bit of the "show ip route" as requested.

!
router eigrp 201
passive-interface default
no passive-interface Vlan22
network 137.1.5.0 0.0.0.255
network 137.1.6.0 0.0.3.255
network 137.1.20.0 0.0.0.255
network 192.168.1.0 0.0.0.15
no auto-summary
!

!

     10.0.0.0/8 is variably subnetted, 21 subnets, 8 masks
C       10.0.0.0/8 is directly connected, Vlan1
D EX    10.50.40.0/23 [170/297270272] via 192.168.*.*, 1w3d, Vlan22
                      [170/297270272] via 192.168.*.#, 1w3d, Vlan22
D EX    10.50.47.0/24 [170/297257472] via 192.168.*.*, 1w5d, Vlan22
                      [170/297257472] via 192.168.*.#, 1w5d, Vlan22
D EX    10.50.32.0/23 [170/297270272] via 192.168.*.*, 2w4d, Vlan22
                      [170/297270272] via 192.168.*.#, 2w4d, Vlan22
D EX    10.50.34.0/25 [170/297270272] via 192.168.*.*, 2w4d, Vlan22
                      [170/297270272] via 192.168.*.#, 2w4d, Vlan22
D EX    10.50.39.0/25 [170/297270272] via 192.168.*.*, 2w4d, Vlan22
                      [170/297270272] via 192.168.*.#, 2w4d, Vlan22
D EX    10.50.70.0/29 [170/297257472] via 192.168.*.*, 1w5d, Vlan22
                      [170/297257472] via 192.168.*.#, 1w5d, Vlan22
D EX    10.50.58.128/27 [170/297257472] via 192.168.*.*, 1w5d, Vlan22
                        [170/297257472] via 192.168.*.#, 1w5d, Vlan22
D EX    10.50.71.248/29 [170/297257472] via 192.168.*.*, 1w5d, Vlan22
                        [170/297257472] via 192.168.*.#, 1w5d, Vlan22
D EX    10.50.71.232/29 [170/297257472] via 192.168.*.*, 6d20h, Vlan22
                        [170/297257472] via 192.168.*.#, 6d20h, Vlan22
D EX    10.50.46.192/26 [170/297257472] via 192.168.*.*, 1w5d, Vlan22
                        [170/297257472] via 192.168.*.#, 1w5d, Vlan22

I have slightly sanitised the results and removed some of the subnets but they are all very similar just not 10.50.?.? addresses.

Once again many thanks

Nick

[cadet alain]

So you want to see a default route advertised by another router/switch and you don't see it, that's your problem?

But that default route if it is advertised it must be with a routing protocol?

Can you post your topology and indicate which routes you are not getting in your rib.

Regards.

[nmjones]

Hi cadetalain,

No I have a default route on the switch set statically and this works normally for anything that isn't in the routing table. My issue is that I hav some 10.X.X.X addresses being learnt via EIGRP which have to route one way and the remaining subnets that dont appear via EIGRP need to route towards my default route, but appear not to be doing they just seem to be in limbo!

As soon as was mentioned higher up the thread about "IP Classless" this fitted my problem perfectly and made perfect sense, but when I checked the config earlier IP Classless is already there

My only other thought is that this config had been translated from a CATOS to IOS when we upgraded the chassis and SUP engines, so I will trawl through it again to see if there are any rogue entries that could cause conflict when inserted to the later config.

Thanks again for taking the time to look.

Nick

[vdadlaney]

Hi Nick,

Can you post a "show ip route x.x.x.x" for the network that you are having a problem with (The one which is supposed to follow the default route). If its not in the routing table than there should be no output for that specific route and also it must show the default entry. In addition can you post the exact config for the default static route that is configured and also the show ip route 0.0.0.0.

Just a thought but could it be that the subnet you are trying to reach is a smaller portion of a larger route that is already in the table and hence its not following the default route but the longest match for that subnet for ex if you are trying to reach 10.100.100.0/26 and there is a entry in the Routing table for 10.100.100.0/24. This is just a guess so do apologize if this is not the case. Thx

Regards,

Vikram

[vdadlaney]

Hi Nick,

I just noticed something in your post previously. Can you pls confirm the ip address configured on VLAN1 and the mask. The output of the show ip route that you posted says

     10.0.0.0/8 is variably subnetted, 21 subnets, 8 masks
C      10.0.0.0/8 is directly connected, Vlan1

If you are trying to reach a subnet 10.x.x.x than all traffic would follow this route and not the default route. Thx

[nmjones]

Vdadlaney great call and well spotted I had totally missed that one! You are absolutely right the switch wouldn't bother trying to forward a packet to the default route as it is a directly connected network.

Vlan 1 indeed does have a class A 10 address configured on it! This must be a legacy thing from before the network was added to a WAN, just an unlucky choice of private addressing coupled with a poor understanding of subnetting

I have submitted a change request now to get them changed ASAP, but I'm pretty confident your on the money and will post a reply once its done with the result.

Once again thank you.

Nick

[nmjones]

Sorry for the delay ... but thanks Vdadlaney you were indeed correct. Altered the subnet mask for all devices and everything now works.

Thanks once again for taking the time to look at my problem.

All the best

Nick