IOS incompatibility between 12.4 and 15.0 causing dropped packets ?

[dlance]

We have a WAN using mpls with 3 of the 2811 routers running IOS 12.4. Recently we tried replacing one of the 2811's with a 2951 running IOS 15.0. During testing we discovered many dropped packets to the remote 2811 routers. Also their CPU usage seems higher then normal. We are using IPSEC encryption on the multilink tunnel. Switching back to the old 2811 and everything returns to normal.

[Calin C.]

Hello,

Where do you see dropped packets? In show output of QoS configuration, physical interface counters...?

On the 2811 you have AIM card or you do IPsec on software? The difference between the two series is that the 2900 has embedded hardware encryption which supposed to perform better than AIM cards:

http://www.cisco.com/en/US/prod/collateral/routers/ps10537/data_sheet_c78_553896.html

Embedded hardware encryption acceleration is enhanced to provide higher  scalability, which combined with an optional Cisco IOS Security  license, enables WAN link security and VPN services (both IPSec and SSL  acceleration).
 The onboard encryption hardware replaces and outperforms the advanced integration modules (AIMs) of previous generations.

If you have a lot of traffic on tunnels, I can think of the following scenario in which for some reason 2900 is processing packets faster than 2800 causing inconsistency in end-to-end traffic.

Anyway, I think the issue is platform related and not an IOS issue. Is true that there are some differences between 12.4 and 15.0, but not in that way that packets could be dropped.

Let me know if you found what's causing this issue.

Cheers,

Calin

[dlance]

Please disregard

It wasnt a problem with the routers at all.

Turned out to be a cable issue when switching from the 100 meg ethernet on the 2811 to the gig ethernet on the 2951

problem solved

the lost packets were at the ethernet of the 2951