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CEF broken - populating the FIB with all internet

Hello,

I'm in serious trouble with a 4948 we are using to both route between our vlans and connect to the internet. We use a default route to our provider through a routed interface, and the rest of our machines are attached to different vlans. When we connect to our provider's switch, the CEF table begins to populate with addresses belonging not just to our LAN, but to any other network out there in internet. In five minutes, CEF has collapsed, begins routing in soft, packets are dropped and 10 min later, the router resets itself. The 4948 has 32000 entries max in the FIB, but, with a default route, it's supposed to be enough for us.

I can't understand this behaviour. Why does the /32 prefixes from all over Internet appear in our FIB? The routing table is the usual one: some entries for the VLAN interfaces, and a default static route to the rest of the world.

Please, I really need help.

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: CEF broken - populating the FIB with all internet

Eladio,

As Richard has already stated, the issue is definitely tied to the fact that you are using a static route pointing to an interface rather than a next-hop IP address.

I find it strange that you are still having the issue after you changed the static route to use the next-hop IP address. Make sure that you didn't just add a second default route but that you also removed the old one that points to the interface.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
11 REPLIES

Re: CEF broken - populating the FIB with all internet

Hi there,

What is the routing protocol that you are running with your provider, i guess that you'll just need to do route filtering allowing only the default route.

HTH,

Mohammed Mahmoud.

New Member

Re: CEF broken - populating the FIB with all internet

That's the point: I'm not using any routing protocol. Just a default route to internet, and connected vlans to the 4948.

Thank you for your replay.

Re: CEF broken - populating the FIB with all internet

Hi there,

Can you post a part of the "show ip route".

BR,

Mohammed Mahmoud.

Hall of Fame Super Silver

Re: CEF broken - populating the FIB with all internet

Eladio

It would be helpful if you would post the static route that is configured. From the symptoms described I wonder if the static route points to the outbound interface rather than to the next hop IP address. If that is the case I suggest that you re-configure the static route so that it specifies the next hop address.

When a static route points just to the outbound interface then the router must resolve each destination address and find the layer 2 address to which the packet should be forwarded. I wonder if this is what is happening to your FIB.

HTH

Rick

New Member

Re: CEF broken - populating the FIB with all internet

Well, we've change the 4948 for a 2821 with 1GB

dram to try to reproduce the problem. We have exactly the same situation, but in this case the 2821 doesn't collapse due to the higher RAM. We've changed, too, the ip route from "ip route 0.0.0.0 0.0.0.0 g0/1" to "ip route 0.0.0.0 0.0.0.0 x.x.x.x", and we keep getting thousands of individual entries for the g1/0 int. And increasing.

By the way, this is the output of the sh adj summ:

g0/1 5736

g0/0.1 3

g0/0.3 1

etc. No one of the other interfaces have more than 256 entries, as they correspond with /24 vlans.

Re: CEF broken - populating the FIB with all internet

Hi Eladio,

Can you paste part of these entries.

BR,

Mohammed Mahmoud.

New Member

Re: CEF broken - populating the FIB with all internet

This are the first ones. There's now another 11500 entries like this in the "sh ip cef"

Prefix Next Hop Interface

0.0.0.0/0 attached GigabitEthernet0/1

attached GigabitEthernet0/1

0.0.0.0/32 receive

4.78.136.18/32 4.78.136.18 GigabitEthernet0/1

4.155.66.8/32 4.155.66.8 GigabitEthernet0/1

4.225.139.30/32 4.225.139.30 GigabitEthernet0/1

8.9.24.24/32 8.9.24.24 GigabitEthernet0/1

8.9.24.25/32 8.9.24.25 GigabitEthernet0/1

12.74.223.54/32 12.74.223.54 GigabitEthernet0/1

12.207.109.175/32 12.207.109.175 GigabitEthernet0/1

12.227.134.111/32 12.227.134.111 GigabitEthernet0/1

13.13.138.219/32 13.13.138.219 GigabitEthernet0/1

15.227.128.53/32 15.227.128.53 GigabitEthernet0/1

16.14.64.50/32 16.14.64.50 GigabitEthernet0/1

16.72.64.50/32 16.72.64.50 GigabitEthernet0/1

17.250.244.61/32 17.250.244.61 GigabitEthernet0/1

17.254.0.23/32 17.254.0.23 GigabitEthernet0/1

17.254.0.34/32 17.254.0.34 GigabitEthernet0/1

18.72.0.3/32 18.72.0.3 GigabitEthernet0/1

24.29.103.10/32 24.29.103.10 GigabitEthernet0/1

24.57.52.67/32 24.57.52.67 GigabitEthernet0/1

24.62.130.231/32 24.62.130.231 GigabitEthernet0/1

24.94.163.100/32 24.94.163.100 GigabitEthernet0/1

24.105.181.196/32 24.105.181.196 GigabitEthernet0/1

24.119.246.205/32 24.119.246.205 GigabitEthernet0/1

24.190.52.80/32 24.190.52.80 GigabitEthernet0/1

24.201.245.37/32 24.201.245.37 GigabitEthernet0/1

24.217.3.83/32 24.217.3.83 GigabitEthernet0/1

BR

Lalo

Cisco Employee

Re: CEF broken - populating the FIB with all internet

Eladio,

As Richard has already stated, the issue is definitely tied to the fact that you are using a static route pointing to an interface rather than a next-hop IP address.

I find it strange that you are still having the issue after you changed the static route to use the next-hop IP address. Make sure that you didn't just add a second default route but that you also removed the old one that points to the interface.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: CEF broken - populating the FIB with all internet

Thank you all of you! Definetly it was that the problem. We added the new default, but didn't erase the old one. Now we have <600 entries int the cef base, stable. We are now going to test the 4948 (after dinner, it's 22:40 in Spain :)) and we'll see how it works. Thanks again everybody!

New Member

Re: CEF broken - populating the FIB with all internet

here you have in its entirity :)

Gateway of last resort is y.y.117.13 to network 0.0.0.0

x.0.0.0/8 is variably subnetted, 30 subnets, 6 masks

S x.x.132.144/28 is directly connected, GigabitEthernet0/0.24

C x.x.128.128/26 is directly connected, GigabitEthernet0/0.4

C x.x.132.136/29 is directly connected, GigabitEthernet0/0.24

C x.x.128.192/26 is directly connected, GigabitEthernet0/0.5

S x.x.130.48/28 is directly connected, GigabitEthernet0/0.29

S x.x.130.32/28 is directly connected, GigabitEthernet0/0.44

C x.x.128.16/29 is directly connected, GigabitEthernet0/0.3

S x.x.130.16/29 is directly connected, GigabitEthernet0/0.57

S x.x.130.16/28 is directly connected, GigabitEthernet0/0.57

C x.x.128.24/29 is directly connected, GigabitEthernet0/0.2

C x.x.128.0/28 is directly connected, GigabitEthernet0/0.1

C x.x.129.0/24 is directly connected, GigabitEthernet0/0.6

S x.x.130.0/29 is directly connected, GigabitEthernet0/0.113

C x.x.131.0/24 is directly connected, GigabitEthernet0/0.18

C x.x.132.0/26 is directly connected, GigabitEthernet0/0.21

C x.x.133.0/24 is directly connected, GigabitEthernet0/0.25

C x.x.134.0/24 is directly connected, GigabitEthernet0/0.29

S x.x.143.8/29 is directly connected, GigabitEthernet0/0.2

C x.x.135.0/24 is directly connected, GigabitEthernet0/0.44

C x.x.136.0/24 is directly connected, GigabitEthernet0/0.216

C x.x.137.0/24 is directly connected, GigabitEthernet0/0.217

C x.x.138.0/24 is directly connected, GigabitEthernet0/0.218

S x.x.130.8/29 is directly connected, GigabitEthernet0/0.218

C x.x.139.0/24 is directly connected, GigabitEthernet0/0.57

C x.x.140.0/24 is directly connected, GigabitEthernet0/0.108

C x.x.141.0/24 is directly connected, GigabitEthernet0/0.113

C x.x.142.0/24 is directly connected, GigabitEthernet0/0.187

C x.x.143.0/30 is directly connected, GigabitEthernet0/0.159

C x.x.128.96/27 is directly connected, GigabitEthernet0/0.225

C x.x.128.64/27 is directly connected, GigabitEthernet0/0.224

y.y.117.0/30 is subnetted, 1 subnets

C y.y.117.12 is directly connected, GigabitEthernet0/1

S* 0.0.0.0/0 [1/0] via y.y.117.13

is directly connected, GigabitEthernet0/1

Cisco Employee

Re: CEF broken - populating the FIB with all internet

If you do a "show ip cef summ" repeatedly, do you see the routes incrementing?

Also, can you do a "show ip cef 192.168.255.1" and please post the output.

Thanks,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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