[c-nsp] MPLS affecting normal IP cache flows

[Andy Saykao]

Hi All,
 
I've deployed MPLS across parts of our core network and everything
appears to be working fine. I've also got MPLS VPN's going which is the
main reason for us rolling out MPLs in the first place.
 
However, I've run into a problem with netflow on one of the PE routers
that affects normal IP flows when mpls is enabled on the interface. The
PE router having this problems is a cisco 7206VXR (NPE-G1) running IOS
Version 12.3(22). Other PE routers are not showing this problem but they
are 7301's running a different IOS.
 
What I'm finding is that when I enable "tag-switching ip" on interface
Gi0/2 which forms part of our MPLS core (as seen below), the netflows
for normal IP traffic isn't as it should be. Doing a "show ip cache
flow" on the PE router only shows a few flows going through for normal
IP traffic and we'd expect more IP cache flows to be going through
because lots of customers hang off this PE router. When we remove the
"tag-switching ip" from the interface, flows are back to normal. 
 
interface GigabitEthernet0/2
 mtu 1500
 ip address 203.10.110.x 255.255.255.224
 ip route-cache flow
 load-interval 30
 duplex full
 speed 1000
 media-type rj45
 no negotiation auto
 tag-switching mtu 1508
 tag-switching ip
 no clns route-cache
 
We are also seeing this in the file size on the netflow collector. After
enabling mpls on interface Gi0/2 above on July 29th, you can see that
from that time on the file size of flows being collected at 12pm is
considerable less than what we would expect.
> ls -la *12-2.bz2
-rw-r--r-- 1 root wheel 29224597 Jul 21 12:59 Netstat_2008072112-2.bz2
-rw-r--r-- 1 root wheel 30218681 Jul 22 12:59 Netstat_2008072212-2.bz2
-rw-r--r-- 1 root wheel 28635436 Jul 23 12:59 Netstat_2008072312-2.bz2
-rw-r--r-- 1 root wheel 26987099 Jul 24 12:59 Netstat_2008072412-2.bz2
-rw-r--r-- 1 root wheel 26003303 Jul 25 12:59 Netstat_2008072512-2.bz2
-rw-r--r-- 1 root wheel 4427493 Jul 26 12:59 Netstat_2008072612-2.bz2
-rw-r--r-- 1 root wheel 4758483 Jul 27 12:59 Netstat_2008072712-2.bz2
-rw-r--r-- 1 root wheel 28679702 Jul 28 12:59 Netstat_2008072812-2.bz2
-rw-r--r-- 1 root wheel 222144 Jul 29 12:59 Netstat_2008072912-2.bz2
-rw-r--r-- 1 root wheel 154352 Jul 30 12:59 Netstat_2008073012-2.bz2
-rw-r--r-- 1 root wheel 315422 Jul 31 12:59 Netstat_2008073112-2.bz2
-rw-r--r-- 1 root wheel 388378 Aug 1 12:59 Netstat_2008080112-2.bz2
-rw-r--r-- 1 root wheel 145880 Aug 2 12:59 Netstat_2008080212-2.bz2
-rw-r--r-- 1 root wheel 171154 Aug 3 12:59 Netstat_2008080312-2.bz2
-rw-r--r-- 1 root wheel 410493 Aug 4 12:59 Netstat_2008080412-2.bz2
-rw-r--r-- 1 root wheel 326936 Aug 5 12:59 Netstat_2008080512-2.bz2

Any ideas as to why enabling mpls would be affecting normal IP cache
flows? I can only suspect that it's some IOS bug with the IOS we're
running .
 
Thanks. 
 
Andy
 
 
 
 

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