Routing question

pll at lanminds.com pll at lanminds.com
Fri May 9 13:44:30 EDT 2003


In a message dated: Fri, 09 May 2003 13:28:31 EDT
Marc Evans said:

>Do all of the routers on the LANs that you are attached to know how to get
>to BOTH of the CIDR blocks that you are part of? If not, then you could
>say that the LAN routing is broken, or you could say that you need to
>insure that when a packet leaves one of your interfaces that it has that
>interfaces IP address in the source. I bet tcpdump (or equiv) will reveal
>your issue(s) pretty quickly.


The network layout looks like this:
                                          BFR
   --------        ________         ________________
  |  eth0  |------| switch |------>|  10.251.35.1   |
  |        |       --------        |----------------|-------->rest of the world
  |  eth3  |\_____ ________        |________________|
   --------       | switch |------>|  10.251.37.1   |
                                    ----------------

So, yeah, both gateways now about each NIC. AFAICT, there shouldn't 
be any reason why I can't have both NICs configured and accessible 
from 'the rest of the world'.  The only thing I can think of, is that 
with a routing table which looks like this:

    # netstat -rn
    Kernel IP routing table
    Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
    10.241.35.0     0.0.0.0         255.255.255.0   U        40 0          0 eth0
    10.241.37.0     0.0.0.0         255.255.255.0   U        40 0          0 eth3
    127.0.0.0       0.0.0.0         255.0.0.0       U        40 0          0 lo
    0.0.0.0         10.241.37.1     0.0.0.0         UG       40 0          0 eth3
    0.0.0.0         10.241.35.1     0.0.0.0         UG       40 0          0 eth0

is that when trying to access something off either of these subnets, 
the system can't figure out which 'default' to take.  Though you'd 
think it would just lob the packets out either one and wait to see if 
it receives an ICMP-redirect from that gateway if it's the wrong one.


                   --------
-- 

Seeya,
Paul
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