2.4.19 ICMP redirects erroneously ignored
I'm getting pounded by ICMP redirects from my Nortel router. The setup is a SuSE 8.1 (2.4.19) standard client with fixed IP and netmask. The client is configured with a default route. However, there are several routers on the subnet that the default router knows about. Hence, the reason that the Nortel router emits ICMP redirects which my client steadfastly ignores.
I've RTFM, read the kernel source, and checked the relevant settings (/proc/sys/net/ipv4/conf/all/*). I find in /proc/net/rt_cache that there are 2 entries, one of which is marked RTCF_REDIRECTED.
Why isn't this redirected route being used?
This seems like a problem that ought to be common to anyone that has multiple routers on the same subnet. What am I missing?
rtg
Quoted 7 lines · Tim Gardner
I'm getting pounded by ICMP redirects from my Nortel router. The setup is a SuSE 8.1 (2.4.19) standard client with fixed IP and netmask. The client is configured with a default route. However, there are several routers on the subnet that the default router knows about. Hence, the reason that the Nortel router emits ICMP redirects which my client steadfastly ignores.
Quoted 5 lines
I've RTFM, read the kernel source, and checked the relevant settings (
/proc/sys/net/ipv4/conf/all/*). I find in/proc/net/rt_cachethat there are 2 entries, one of which is markedRTCF_REDIRECTED.Why isn't this redirected route being used?
AFAIK, because that would mean that you are allowing another machine to manipulate your routing tables by simply using ICMP. How do you know that you can trust the other machine, in this case, the nortel router ? The problem is not of (missing) functionality, its about trusting the integrity of the source of the ICMP redirect.
Quoted 10 lines
This seems like a problem that ought to be common to anyone that has multiple routers on the same subnet. What am I missing?
rtg
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Signature · 5 lines
Ranjeet Shetye Senior Software Engineer Zultys Technologies Ranjeet dot Shetye2 at Zultys dot com http://www.zultys.com/
I understand the ramifications of ICMP redirect and how it can be mis-used. However, the SuSE 8.1 default for non-forwarding (/proc/sys/net/ipv4ip_forward==0) Linux is to accept redirects. I also own the router, so I trust it.
rtg
Quoted 29 lines · Ranjeet Shetye
Quoted 7 lines · Tim Gardner
I'm getting pounded by ICMP redirects from my Nortel router. The setup is a SuSE 8.1 (2.4.19) standard client with fixed IP and netmask. The client is configured with a default route. However, there are several routers on the subnet that the default router knows about. Hence, the reason that the Nortel router emits ICMP redirects which my client steadfastly ignores.
Quoted 5 lines
I've RTFM, read the kernel source, and checked the relevant settings (
/proc/sys/net/ipv4/conf/all/*). I find in/proc/net/rt_cachethat there are 2 entries, one of which is markedRTCF_REDIRECTED.Why isn't this redirected route being used?
AFAIK, because that would mean that you are allowing another machine to manipulate your routing tables by simply using ICMP. How do you know that you can trust the other machine, in this case, the nortel router ? The problem is not of (missing) functionality, its about trusting the integrity of the source of the ICMP redirect.
Quoted 9 lines
This seems like a problem that ought to be common to anyone that has multiple routers on the same subnet. What am I missing?
rtg
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Signature · 3 lines
Tim Gardner - [email protected] 406-443-5357 TriplePoint, Inc. - http://www.tpi.com PGP: http://www.tpi.com/PGP/Tim.txt