Slow connection over a Low speed serial link on 1841

Unanswered Question
Aug 6th, 2008

I have a 1841 Cisco Router with 2 Low speed Serial link ports (one of them is currently used) which show a lot of latency. The traceroute over that hop (the serial link) is around a 1000 ms vs the other hops which is just 4-5 ms. The clockrate is set to 128000 for some reason I cant understand (It was set by someone else). Please let me know is there something I can do to improve this latency...

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Wed, 08/06/2008 - 08:23

Hello Uzma,

verify if you serial link is congested with:

sh int serial x/y

look for output drops

input errors

verify if they are increasing over time

the clockrate on an A/S interface cannot be set to 2Mbps when used as Sync Serial but up to 128000 so this is fine.

May be the router is performing load-balancing among links of different speeds

depending on the routing protocol in use (if any ) you need to make this link less preferred then the other links (again if any exists)

Hope to help


uzmausmani Mon, 08/11/2008 - 14:58

I checked the output drops. They are quite a lot and there are input errors on the router to which it is connected to over the serial link (Cisco 7200). There is only one active serial link so its not performing any load balancing. In fact I was thinking of aggregating the bandwidths on the the two serial ports. Would that help improve latency? there are no routing protocols in use...only static routes. One thing I noticed is that the low speed serial link on the 1841 is connected to a high speed serial link on a 7200. Does that matter?

Giuseppe Larosa Tue, 08/12/2008 - 00:28

Hello Uzma,

there is too much traffic for this link.

Adding a parallel link will improve the performance and should reduce latency.

If the high speed serial on C7200 is set for 128 kbps by accepting the line clock or providing it (clock rate command) it is fine.

Hope to help



This Discussion