[nsp] CEF problem on 6509 (native)

Jack.W.Parks at alltel.com Jack.W.Parks at alltel.com
Wed Nov 12 22:42:14 EST 2003

Did you happen to readdress the link with a new IP address?  For
example:  The link toward the CMTS was, but recently you
changed it to

We have had many problems related to this type of change and CEF.  The
ONLY fix was to reload the router after any destination next-hop change.


Jack W. Parks IV
Sr. Network Engineer
ALLTEL Communications
jack.w.parks at remove-me.alltel.com
Work: 501-905-5961
Cell: 501-680-3341

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Sorin
Sent: Wednesday, November 12, 2003 1:42 PM
To: cisco-nsp at puck.nether.net
Subject: Re: [nsp] CEF problem on 6509 (native)


I found out what the problem is (with some help from the list), but i
don't know how i can get rid of it.

The router has a mls cef entry for x.y.z.25 different from x.y.z.0/24,
when in the routing table i have only entry, for x.y.z.0/24:

r2#show mls cef x.y.z.0

Index      Prefix           Mask                Adjacency
13429      x.y.z.0       00d0.0568.980a
r2#show mls cef x.y.z.25

Index      Prefix           Mask                Adjacency
2240       x.y.z.25     00a0.d2a4.5003

This client is connected via a cable-modem. The CMTS is Cuda (router,
not bridge).

I don't get it from where does this router learn that mls cef entry. The
layer3 path is

r2 --> r1 --> CUDA CMTS --> client

I've even monitored CUDA's traffic for 00a0.d2a4.5003 or x.y.z.25 to see
what packets come/go when the mls cef entry is renewed, but i haven't
seen any.

r2 does not have any interface in the vlan in which the CUDA CMTS is

I really don't know what to do next. If there's anything i forgot to
add, please drop pe an email.

adonay at dumnez.eu.org
Linux Registered User #222086

> On 11/11/03 2:35 AM, "Sorin CONSTANTINESCU" <adonay at dumnez.eu.org> 
> wrote:
>> Hi,
>> One of our Cat6500 routers' CEF is acting strangely. The router 
>> wouldn't forward traffic towards x.y.z.25, but it would for x.y.z.26.

>> CEF has an entry for x.y.z/24 (known by the router from BGP).
>> If i put an ACL on a VLAN (in) with permit for x.y.z.25, traffic 
>> coming via that vlan will be routed, but only the traffic coming via 
>> that vlan.
>> The temporary solution was to have a route for x.y.z.25.
>> The 6509 has msfc2/sup2, and runs Version 12.1(19)E (native). I 
>> looked for CEF bugs using cisco's bugtool, but none match
>  my case.
>> Does anybody have a clue on how to solve this problem?
>> Regards,

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