[CentOS] Simple routing question

James B. Byrne byrnejb at harte-lyne.ca
Thu Sep 6 12:11:49 EDT 2012


I am still having some difficulty understanding what is going on with
routing on 192.168.x.x.

I have removed the IP aliases from the gateway eth1 so that it only
responds to aaa.bbb.ccc.1.

I have changed the netmask on Host B eth1 [192.168.209.43] to
255.255.0.0 and set its gateway to aaa.bbb.ccc.1; as I have on all of
the guests that have eth1 active.

The network service on both hosts and guests has been restarted.

However, when I do a traceroute from Host C [aaa.bbb.ccc.25] to
192.168.209.43 it still goes directly to the gateway at aaa.bbb.ccc.1
and thence out to the eth0 i/f on the gateway, where it dies as
before.

I note that Host C is a xen virtual host (used for some experiments
several years ago but no longer hosting any active guests) and that it
has the following virtual interface:

5: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

This has an address in the same network as 192.168.209.43 but with a
different netmask.  This seems to eb the case on the kvm virtual hosts
as well.

6: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue
state UNKNOWN
    link/ether 52:54:00:a6:3f:49 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

So, is this the source of the problem when I try and connect to
192.168.209.43?  Is the netblock 192.168.255.255 constrained to use a
netmask of 255.255.255.0 because of its use by the virtual hosts?

-- 
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James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
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