Date: Sat, 12 Feb 2011 11:36:50 +0200 From: Nikolay Denev <ndenev@gmail.com> To: freebsd-net@freebsd.org Subject: option RADIX_MPATH, RT_LINK_IS_UP() and interface routes. Message-ID: <7C507431-3902-4B7A-B33F-51ECCFFF8306@gmail.com>
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Hello,
A quick glance through sys/netinet/ip_output.c shows that interface =
routes are short-circuited and
not checked for RT_LINK_IS_UP as gateway routes are.
Consider the following scenario :
A pair of redundant routers : RTR1 and RTR2.
Each having dedicated uplink to some ISP and both run BGP, and they also =
have a dedicated cross-connection.
On the LAN side, they share a IP using CARP.
Uplink1 Uplink2
| |
| |
+------+ +------+
| RTR1 |---| RTR2 |
+------+ +------+
| |
| |
+---+----------+---+
| LAN |
+------------------+
Now, if the cable on RTR1 connecting it to the LAN is disconnected,
RTR2 will become carp master and will start receiving packets from =
clients on LAN and they will be routed ok.
But form the ISP point of view the best path to the network is via RTR1, =
so the incoming traffic
will still be routed thru RTR1 because it's Uplink1 interface is UP and =
the BGP session established.
This will cause the packets destined to the LAN to be effectively =
blackholed, because of the interface route on RTR1.
When using kernel with RADIX_MPATH and ospf on both routers RTR1 will =
have two routes to the LAN, one interface and one via
the crossconnect to RTR2 but still, the interface route will be consen, =
regardless of link state up or down.
I'm thinking about checking for RT_LINK_IS_UP on interface routes, or =
clear the RTF_UP flag on those routes when interface goes link down. Any =
other solutions/ideas?
Cheers,
Nikolay
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