Traceroute and WANIP - PPP

This is a discussion on Traceroute and WANIP - PPP ; Hi, I have a PPP link between station A and B with a router at each site. I have configured WAN IP for the routers. When I do a traceroute from a PC in station A to one in station ...

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Thread: Traceroute and WANIP

  1. Traceroute and WANIP

    Hi,

    I have a PPP link between station A and B with a router at each site.
    I have configured WAN IP for the routers.

    When I do a traceroute from a PC in station A to one in station B (or
    vice versa), sometimes one of the two WAN IPs (local WAN or remote
    WAN) is featured in the hop-list. And sometimes I dont see any of the
    WAN IPs at all.

    My question is what decides this behaviour.

    Thanks and regards.
    Prabhu.

  2. Re: Traceroute and WANIP

    ramnath_prabhu@hotmail.com (Ramnath Prabhu) writes:
    > When I do a traceroute from a PC in station A to one in station B (or
    > vice versa), sometimes one of the two WAN IPs (local WAN or remote
    > WAN) is featured in the hop-list. And sometimes I dont see any of the
    > WAN IPs at all.
    >
    > My question is what decides this behaviour.


    The router.

    The way traceroute (typically) works is by sending out a UDP datagram
    to some arbitrary port on the destination host with increasing TTLs.
    The theory is that each router in the middle will decrement the TTL,
    and the one that comes up zero will reply with an ICMP Time Exceeded /
    TTL Exceeded in Transit message (type 11, code 0). The destination
    host should respond with ICMP Destination Unreachable / Port
    Unreachable (type 3, code 3).

    Of course, lots of things can go wrong here. The routers may choose
    different paths for each packet (thus making hash of the returned
    list). The routers may rate limit errors or otherwise decline to
    generate an ICMP error. Some firewalls drop all ICMP messages just of
    of spite. Some tunneling / NAT software can drop, translate, or even
    forge up funny-looking ICMP messages at the boundaries.

    --
    James Carlson, Solaris Networking
    Sun Microsystems / 1 Network Drive 71.234W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.497N Fax +1 781 442 1677

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