Date: Sat, 4 Jan 2003 05:38:58 -0600 (CST) From: Kevin Day <toasty@shell.dragondata.com> To: freebsd-net@freebsd.org Subject: Traceroute through specific gateway/interface Message-ID: <200301041138.h04Bcwe82722@shell.dragondata.com>
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Has anyone ever created a patch for traceroute that lets you force it to go
through a specific interface, or use a certain gateway even if the routing
table says otherwise? I know I can use source routing, but a good percentage
of the routers on the internet drop source routed packets now.
Here's my situation... I have a FreeBSD system running as a router to
multi-home us between three uplinks, with us running Zebra for BGP. It'd be
nice to occasionally take a look at a traceroute through one of the other
uplinks. (other than the one that Zebra has added a route for)
+-----------------------+
| | ISP-A
| bge0 10.1.0.2/30 +----------> 10.1.0.1
| |
| | ISP-B
| bge1 10.2.0.2/30 +----------> 10.2.0.1
| |
| | ISP-C
| bge2 10.3.0.2/30 +----------> 10.3.0.1
| |
LAN | |
<-------+ bge3 10.9.0.254/24 |
+-----------------------+
If Zebra has decided that the route to 192.168.0.1 is shortest through
ISP-A, doing a regular traceroute to 192.168.0.1 goes through ISP-A easily.
If I want to traceroute to that IP through ISP-B, I use the -s traceroute
option to set the source IP address to 10.2.0.2 (to ensure the return path
goes through ISP-B, since only ISP-B is announcing that /30's space). If I
use the -g option to source route the traceroute through 10.2.0.1, it mostly
works, except that if I use source routing, I can't trace route through two
of my uplinks since they disable source routing. Even through the one that
doesn't, I usually hit a router somewhere along the way that has it
disabled.
Any ideas?
-- Kevin
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