Re: OSFP router-id not appearing in traceroute (on 7204VXR)
- From: briggs@xxxxxxxxxxxxxxxxx
- Date: 19 Jul 2007 11:41:12 -0500
In article <1184837189.952968.98100@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Merv <merv.hrabi@xxxxxxxxxx> writes:
On Jul 17, 10:00 am, mrennt <m.re...@xxxxxxx> wrote:
On 17 Jul., 13:29, Merv <merv.hr...@xxxxxxxxxx> wrote:
traceroute in Cisco routers has no knowledge of OSPF.
Traceroute use ICMP echo and echo-reply messages.
The source IP address of the ICMP packet is the "nearest" interface IP
address to the destination IP address being traced
I completely understand that. As there's a route to xx.xx.xx.65 via
10.0.0.1 it uses the local interfaces that is connected to
10.0.0.0/24.
O xx.xx.xx.65/32 [110/2] via 10.0.0.1, 13:59:39,
FastEthernet3/0
While IOS provides the ability to change this behaviour in certain
cases ( for example "ip ftp source-interface") AFAIK this is not
possible for traceroute.
What really bugs me, is that a traceroute to RTC (a linux machine)
does return the actual loopback IP that is traced and not the private
IP.
Why would RTA return 10.0.0.1 in the ICMP reply when the traceroute is
actually directed to xx.xx.xx.65, which is configured on the loopback
interface on RTA?
i.e.
---------------------------------
Traceroute to Cisco Router RTA
---------------------------------
RTB#traceroute xx.xx.xx.65
Type escape sequence to abort.
Tracing the route to xx.xx.xx.65
1 10.0.0.1 [AS xxxx] 0 msec * 0 msec
---------------------------------
Traceroute to equally configured linux router RTC
---------------------------------
RTB#traceroute xx.xx.xx.67
Type escape sequence to abort.
Tracing the route to xx.xx.xx.67
1 xx.xx.xx.67 0 msec 4 msec 0 msec
The address displayed by traceroute is the source address returned in
the ICMP time-exceeded packet.
We're not talking about the ICMP time-exceeded packet produced by
an intermediate gateway.
We're not talking about an ICMP echo-reply packet produced by the
final destination.
We're not talking about an ICMP-based Windows style traceroute.
We're talking about a UDP-based Unix style traceroute
The question at hand is what source IP address is appropriate on the
ICMP unreachable (port unreachable) datagram produced at the final
destination when a UDP datagram arrives for a port on which no application
is listening.
.
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