nanog mailing list archives
Re: loose source route
From: Curtis Villamizar <curtis () ans net>
Date: Thu, 30 Mar 1995 12:05:31 -0500
In message <9503301600.AA01532 () stick NERSC gov>, "Chris Dorsey (510)422-4474" w rites:
I agree with Matt, if a network turns off LSRR, then I try to hand them the ticket. However, it seems that lots of sites either yield no human response at all, or get back to you a few days later. Not very helpful in the face of intermittent problems. So you're the one holding the trouble ticket with no tools and no help. I've thought a little about this over the past few months as more sites shut off LSRR, and it seems like a "ping" or "traceroute" server-client would really come in handy. No human interaction needed, I just request a ping/trace from site A going from A to B. Has anyone explored this or is it a silly idea and I'm being dense. /chris Chris Dorsey ESnet dorsey () es net
If LSRR is turned off somewhere, what I ussually do is the following Start in the middle of your network (anywhere in 140.222 in our case) and traceroute to both sites in question. For each direction: Try a traceroute -g from end site A to end site B (traceroute -g A B). If this never reaches end site A, presumably because LSRR is blocked, then back up to the last router that responded (call it R1). Then traceroute from R1 to B (traceroute -g R1 B). This will often end slightly before B (call this R2). What this usually yields is: /-->- hop hop hop -->-\ A ... R1 -<-- hop hop hop -<-- R2 ... B \ / \ / --- you are here -- This is OK as long as R1 and R2 are very close to the site. They are usually the provider router one hop from the firewall. There may be an assymetric route, with one side going off into the black hole (this is then the problem). There may be a symmetric or assymetric route with a loss problem. Since you now know the route, you can now try source routed ping and try to isolate the loss enough to know which NOC to notify. If the problem is loss between A and R1 or B and R2, then a regular ping should show the problem. The only case where this doesn't work is where the route from A to B or B to A doesn't go through R1 and/or R2. There is no way to know this for sure. I don't know of any IP providers that have turned off LSRR on their backbone routers, just site routers. Curtis
Current thread:
- loose source route C. Philip Wood (Mar 24)
- Re: loose source route Paul Ferguson (Mar 24)
- Re: loose source route roy alcala (Mar 24)
- Re: loose source route Matt Mathis (Mar 30)
- <Possible follow-ups>
- Re: loose source route Vadim Antonov (Mar 27)
- Re: loose source route Paul Traina (Mar 27)
- Re: loose source route bmanning (Mar 27)
- Re: loose source route Chris Dorsey (510)422-4474 (Mar 30)
- Re: loose source route Hans-Werner Braun (Mar 30)
- Re: loose source route Chris Dorsey (510)422-4474 (Mar 30)
- Re: loose source route Curtis Villamizar (Mar 30)
- Re: loose source route Hans-Werner Braun (Mar 30)
- Re: loose source route Paul Ferguson (Mar 24)