I have had this problem on and off since RedHat 6, and I always worked through it, but I thought I would ask. When you have multiple network interfaces, how does the system determine the default route? Or is it the first, (or last) interface that comes up?
On the problem systems I have to add a "route add default..." statement in some systems in the rc.local to get them to work right.
Edit /etc/sysconfig/network add GATEWAY=xxx.xxx.xxx.xxx
2006/4/7, Scott Silva ssilva@sgvwater.com:
I have had this problem on and off since RedHat 6, and I always worked through it, but I thought I would ask. When you have multiple network interfaces, how does the system determine the default route? Or is it the first, (or last) interface that comes up?
On the problem systems I have to add a "route add default..." statement in some systems in the rc.local to get them to work right.
--
MailScanner is like deodorant... You hope everybody uses it, and you notice quickly if they don't!!!!
CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
-- ===================== Marcus Tulio T. Carvalho Telemacro Sistemas e Serviços =====================
Marcus Carvalho spake the following on 4/7/2006 1:37 PM:
Edit /etc/sysconfig/network add GATEWAY=xxx.xxx.xxx.xxx
2006/4/7, Scott Silva <ssilva@sgvwater.com mailto:ssilva@sgvwater.com>:
I have had this problem on and off since RedHat 6, and I always worked through it, but I thought I would ask. When you have multiple network interfaces, how does the system determine the default route? Or is it the first, (or last) interface that comes up? On the problem systems I have to add a "route add default..." statement in some systems in the rc.local to get them to work right.
I have done that, but it still seems to have a mind of its own. Does the gateway statement mater where it is in the file? IE... could it be the second statement instead of the last?
Scott Silva wrote:
I have done that, but it still seems to have a mind of its own. Does the gateway statement mater where it is in the file? IE... could it be the second statement instead of the last?
The route is chosen according to the cost associated with the route. If the gateway is an IP address the cost will be 1, if it is an interface the cost will be 0. The route with the lowest cost will be used. You can have more than 1 gateway.
http://www.comptechdoc.org/os/linux/usersguide/linux_ugrouting.html
What does the command "route" says?
centos@911networks.com spake the following on 4/7/2006 3:23 PM:
Scott Silva wrote:
I have done that, but it still seems to have a mind of its own. Does the gateway statement mater where it is in the file? IE... could it be the second statement instead of the last?
The route is chosen according to the cost associated with the route. If the gateway is an IP address the cost will be 1, if it is an interface the cost will be 0. The route with the lowest cost will be used. You can have more than 1 gateway.
http://www.comptechdoc.org/os/linux/usersguide/linux_ugrouting.html
What does the command "route" says?
I seem to have fixed it by not giving the internal network route a gateway, since it doesn't need to reach anything but the internal network. I just wish it was smart enough to "see" where a packet came from and reply over the same route.
Marcus Carvalho spake the following on 4/7/2006 1:37 PM:
Edit /etc/sysconfig/network add GATEWAY=xxx.xxx.xxx.xxx
2006/4/7, Scott Silva <ssilva@sgvwater.com mailto:ssilva@sgvwater.com>:
I have had this problem on and off since RedHat 6, and I always worked through it, but I thought I would ask. When you have multiple network interfaces, how does the system determine the default route? Or is it the first, (or last) interface that comes up? On the problem systems I have to add a "route add default..." statement in some systems in the rc.local to get them to work right.
GATEWAY is a bash variable - so whoever sets it last wins. I would recommend putting it in /etc/sysconfig/network .. I would also make sure that there are no files in /etc/sysconfig/networking or in /etc/sysconfig/networking/profiles/default .. these get read after the /etc/sysconfig/network-scripts files .. and as I mentioned before - whoever sets it last, wins.
Barry
Scott Silva wrote:
I have had this problem on and off since RedHat 6, and I always worked through it, but I thought I would ask. When you have multiple network interfaces, how does the system determine the default route? Or is it the first, (or last) interface that comes up?
On the problem systems I have to add a "route add default..." statement in some systems in the rc.local to get them to work right.
You can add a default route into /etc/sysconfig/network, and the network with the matching network ip will take the route.
If you have more that one default route capability on different interfaces, you can set up routing tables for each of the networks , and then apply a weighting to each network default route in the main routing table...
There is an excellent discussion on it here, that answers your later question about sending out packets on the right interface.
http://lartc.org/howto/lartc.rpdb.multiple-links.html
If you follow the guidlines in this document but only add a default route to your main preferred gateway all traffic outgoing will be routed to that gateway but replies topackets on the other interfaces will still be serviced via the default routes on those interfaces if they come from networks outside the network ranges of all the network interfaces on the box....
If you want more detail, send me your ip ranges and ips and I will send you a set of ip rules/routes to achieve what you want...
Regards
Pete
-
Barry Brimer -
centos＠911networks.com -
Marcus Carvalho -
Peter Farrow -
Scott Silva