01-25-2009 01:53 AM - edited 03-06-2019 03:38 AM
Over the years I have observed that the command
router#traceroute ip xxx.xxx.xxx.xxx
when used on 800, 1700 and 1800 series routers, returns route information extremely slowly. What normally takes second when executed on a host, takes virtually minutes on these routers.
Does anyone know why?
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01-25-2009 08:28 AM
Louie,
This could be due to the fact that the traceroute will try to do a DNS reverse name lookup by default. This can add quite a bit to the traceroute, especially if you don't have a DNS server configured on the router. Try "no ip domain-lookup" in global configuration mode and retry the traceroute.
Regards
01-25-2009 02:27 AM
Probably because when you are doing trace from Cisco router its sending UDP packets for the trace.
But when doing a atraceroute from a host(windows pc etc.) its using ICMP.
01-25-2009 03:00 AM
Thank you for your input. While I would certainly expect the latency for UDP traffic to be greater than ICMP traffic, the traceroute response difference between pc's and routers is orders of magnitude.
I wonder if there are not other contributing factors.
01-25-2009 08:28 AM
Louie,
This could be due to the fact that the traceroute will try to do a DNS reverse name lookup by default. This can add quite a bit to the traceroute, especially if you don't have a DNS server configured on the router. Try "no ip domain-lookup" in global configuration mode and retry the traceroute.
Regards
01-26-2009 07:19 AM
Thanks Harold. It completely solves the problem.
01-26-2009 10:29 PM
This could be due to the fact that the traceroute will try to do a DNS reverse name lookup by default ?
What it means plz explain in brief
01-27-2009 07:29 AM
Kaustubh,
It means that this command will send a reverse DNS lookup request (IP address to host) to the DNS server. If "ip domain-lookup" is configured and "ip name-server" is not, the DNS request is sent to the broadcast ip address (255.255.255.255). This obviously cause some delay in the command, unless there is a DNS server directly connected to the router.
Regards
01-27-2009 07:38 AM
Just as a precision, if the reverse DNS lookup succeeds, you should get the hostname in the output of the traceroute as follow:
r1#trace 192.168.4.1
Type escape sequence to abort.
Tracing the route to 192.168.4.1
1 R2 (192.168.12.2) 20 msec 20 msec 52 msec
2 R3 (192.168.23.2) 20 msec 20 msec 20 msec
3 R4 (192.168.34.2) 32 msec * 28 msec
r1#
Regards
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