[CentOS] Simple routing question

Les Mikesell lesmikesell at gmail.com
Thu Sep 6 14:20:43 EDT 2012


On Thu, Sep 6, 2012 at 1:09 PM, James B. Byrne <byrnejb at harte-lyne.ca> wrote:
>
>> A 'route -n' should show you where any destination will head
>> on the next hop.  On host C, what is the line with the
>> smallest matching destination/mask?  Likewise, on the gateway
>> host where you think it is being forwarded the wrong way?
>
>
> $ /sbin/route -n
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref
> Use Iface
> 192.168.122.0   0.0.0.0         255.255.255.0   U     0      0
> 0 virbr0
> aaa.bbb.ccc.0    0.0.0.0        255.255.255.0   U     0      0
> 0 bridge0
> 169.254.0.0     0.0.0.0         255.255.0.0     U     0      0
> 0 bridge0
> 0.0.0.0         aaa.1bbb.ccc.1  0.0.0.0         UG    0      0
> 0 bridge0
>
>
> $ traceroute 192.168.209.43
> traceroute to 192.168.209.43 (192.168.209.43), 30 hops max, 40 byte
> packets
>  1  gway01 (aaa.bbb.ccc.1)  0.321 ms  0.298 ms  0.283 ms

OK, there is no better match than the default in the route table
above, so it goes to the default gateway.  I assume that's what you
want if you don't make the netmask span the 192.168.x.x range, but a
side effect is that it will source from the aaa.bbb.ccc.x interface
address.

> This seems to say that 192.168.209.43 is being routed out to the
> Internet as aaa.bbb.ddd.53 is our external gateway address on the
> router.
>
> This is the routing table on the router:
>
> [root at gway01 ~]# route -n
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref
> Use Iface
> aaa.bbb.ddd.52  0.0.0.0         255.255.255.252 U     0      0
> 0 eth0
> aaa.bbb.ccc.0   0.0.0.0         255.255.255.0   U     0      0
> 0 eth1
> 169.254.0.0     0.0.0.0         255.255.0.0     U     1002   0
> 0 eth0
> 169.254.0.0     0.0.0.0         255.255.0.0     U     1003   0
> 0 eth1
> 0.0.0.0         aaa.bbb.ddd.53  0.0.0.0         UG    0      0
> 0 eth0

I don't see any 192.168.x.x interface/mask there.   Where else could
it go?   Or is that 2nd 169.254.0.0 a typo?

-- 
   Les Mikesell
     lesmikesell at gmail.com


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