[ale] Fun routing

[James Sumners]

I didn't see this since ALE stuff started going to SPAM (that is being
resolved). I had to settle for putting everything on a single bond
interface and forgetting about a service interface. I had to get the
systems operational.

On Wed, Oct 11, 2017 at 4:47 PM, Ed Cashin <ecashin at noserose.net> wrote:

> One thing to bear in mind is that with many Linux systems in a default
> configuration, ARP replies will mention an inaccessible IP address.
>
> E.g., host A on networks 1 and 2 has interfaces A1 and A2.  Host B is only
> on network 2.  Say A1 has IP 10.1.1.1 with MAC address aa:bb:cc:dd:ee:ff.
>
> Now do "arping -I B2 10.1.1.1" on B.  Even though that's the IP for A1,
> which B cannot get to directly, A responds with an ARP reply that says
> aa:bb:cc:dd:ee:ff has IP 10.1.1.1.
>
>
>
> On Wed, Oct 11, 2017 at 4:06 PM, James Sumners <james.sumners at gmail.com>
> wrote:
>
>> I lied. I'm not having fun.
>>
>> I have a system with three NICs: eth0, eth1, eth2. This system is to be a
>> "load balancer," or, more accurately, a reverse proxy for many end points.
>> My desire is to make eth0 a "maintenance" NIC and bond eth1 & eth2 into the
>> primary service interface, bond0. I have three subnets in play:
>> 10.0.1.0/24, 10.0.2.0/24, and 10.0.3.0/24. Pretend that 10.0.2/24 and
>> 10.0.3/24 are public, Internet accessible, subnets and 10.0.1/24 is
>> private. The proxy will serve end points on all three of these subnets.
>>
>> Okay, so let's setup the interfaces:
>>
>> ```
>> $ echo -e "1 service\n2 bond" >> /etc/iproute2/rt_tables
>>
>> $ ip link set eth0 up
>> $ ip addr add 10.0.1.2/24 dev eth0
>> $ ip rule add iif eth0 prio 0 table service
>> $ ip route add to 0.0.0.0/0 via 10.0.1.1 dev eth0 prio 10000 table main
>> $ ip route add default via 10.0.1.1 dev eth0 table service
>> $ ip route flush cache
>>
>> $ ip link add dev bond0 address 00:00:00:aa:bb:cc type bond
>> $ echo balance-alb > /sys/class/net/bond0/bonding/mode
>> $ echo 100 > /sys/class/net/bond0/bonding/miimon
>> $ ip link set eth1 master bond0
>> $ ip link set eth2 master bond0
>> $ ip link set bond0 up
>> $ ip addr add 10.0.2.2/24 dev bond0 # see note 1 below
>> $ ip rule add iif bond0 prio 0 table bond
>> $ ip route add default via 10.0.2.1 dev bond0 table bond
>> $ ip route flush cache
>> ```
>>
>> Cool. Now let's add an end point:
>>
>> ```
>> $ ip addr add 10.0.3.15/32 dev bond0
>> ```
>>
>> So, what's the problem? The switches see 10.0.3.15 as being associated
>> with eth0. Thus, things don't work correctly. I can use tcpdump to monitor
>> the traffic on bond0, ping 10.0.3.15 and see the traffic come in, but the
>> pinger never gets a pong.
>>
>> At this point I'm probably just going to say to hell with the maintenance
>> interface and have all traffic on the bond and routed with the main table.
>> But I figured I'd see if anyone has any guesses about why this
>> configuration isn't working. To the best of my knowledge, the following
>> should be true:
>>
>> 1. Traffic originating on the system will be routed through 10.0.1.1 via
>> the eth0 interface as per the "main" routing table.
>> 2. Traffic originating remotely via 10.0.1.2 will route through 10.0.1.1
>> via the eth0 interface as per the "service" routing table.
>> 3. Traffic originating remotely via 10.0.2.2 or 10.0.3.15 will route
>> through 10.0.2.1 via the bond0 interface as per the "bond" routing table.
>>
>> Note 1: this is actually a pair of systems configured for failover with
>> Ucarp as provided by https://github.com/jsumners/ucarp-rhel7 . Ucarp
>> needs a "master IP" to tie the VIPs to.
>>
>> --
>> James Sumners
>> http://james.sumners.info/ (technical profile)
>> http://jrfom.com/ (personal site)
>> http://haplo.bandcamp.com/ (music)
>>
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>>
>>
>
>
> --
>   Ed Cashin <ecashin at noserose.net>
>
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> http://mail.ale.org/mailman/listinfo
>
>


-- 
James Sumners
http://james.sumners.info/ (technical profile)
http://jrfom.com/ (personal site)
http://haplo.bandcamp.com/ (music)
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