Input overrun errors in 2901 router

[shlomiohana101]

Greetings. (Sorry for my english)

A few days ago I purchased from eBay a used 2901 router.

The router came with only two built-in connections (g0 / 0 g0 / 1) with no ehwic extensions.

I connected the router to a home router that provides a 1gbps fiber connection.

I reset the 2901 and made all the settings (ip addresses, nat, etc.).

Ping tests, web browsing, ssh, no problems, but i noticed the problem when I did a Speed Test: instead of getting 1gbps, I get around 300mbps from the 2901, when in a direct connection to my home router I get always 1gbps without any problems.

When I examined the issue a little more in depth, I noticed that I get a lot of input overrun errors in the two built-in connections of the router (g0 / 0 and g0 / 1).

I tried to switch cables, switch between interfaces, perform a software update to the router, connect to it directly, and for some reason I always get input overrun errors.

I wanted to ask, is this a malfunction of the interfaces? (i.e. buying ehwic will solve the problem) or is the problem in the main board? Please See the screen recording that describing the problem.

Thank you

[Giuseppe Larosa · Accepted solution]

Hello ,

what you get is normal for a C2901 even if it has two buiilt in GE interfaces it has never been meant to be able to work at line rate full 1 Gbps.

overrun error means that packets are arriving on the interface at a speed greater then interface capabilities so these packets are dropped.

There is nothing you can do about it.

It is normal and it is not a sign of an hardware problem just a sign of a performance limit.

Hope to help

Giuseppe

[shlomiohana101]

Thank you very much for the detailed answer. You helped me a lot, and as a beginner I learned a very important lesson about router performance. (Very important for the next purchase)

[Leo Laohoo · Accepted solution]

2900 router is not designed to support >100 Mbps.  

Input Overruns happen when the router is unable to process the inbound traffic and drops the packets.

Either get a bigger router or downgrade the WAN link.

[Kevin Kilgore]

I don't know of any routers that route at line speed. However a layer 3 switch will.

[Joseph W. Doherty]

Kevin there are routers that can route at line speed and also some L3 switches that cannot.

The usual situation is often "smaller" routers have a port that exceeds the performance capacity of the router while many switches can support line speed on at least some of their ports although, sometimes, not on all ports concurrently.