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why is traceroute so slow?

cisco-admins
Level 1
Level 1

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?

1 Accepted Solution

Accepted Solutions

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

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

View solution in original post

7 Replies 7

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.

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.

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

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Thanks Harold. It completely solves the problem.

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

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

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

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

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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