[Click] XORP+Click Hotconfig

[Pavlin Radoslavov]

> I am trying to implement hotswap in my xorp+click test bed. However, it is 
> not functioning correctly. I would appreciate if I get some help to fix 
> this issue. Here is what I am trying to do...
> 
> Network configuration
> ---------------------
> 
> 
> PC 1---------ROUTER1------ROUTER2--------PC 2
>             eth4  eth3   eth1  eth2
> 
> Where Router1 and Router2 are both running Xorp+click. The xorp config file 
> has the following entry...
> 
> user-click {
> 	disable: false
> 	command-file: "/home/eessd/click/bin/click"
> 	command-extra-arguments: "-R"
> 	command-execute-on-startup: true
> 	control-address: 127.0.0.1
> 	control-socket-port: 13000
> 	startup-config-file: "/dev/null"
> 	user-click-config-generator-file: 
> "/usr/localxorp/fea/xorp_fea_click_config"
> }

First, a small observation: I presume that
"/usr/localxorp/fea/xorp_fea_click_config" is either a typo
(in your configuration the correct value is
"/usr/local/xorp/fea/xorp_fea_click_config"), or that your XORP
installation is indeed in the "/usr/localxorp" directory.

> Given the above all is well and I can ping PC2 from PC1 with the above 
> configuration.
> 
> Now, I try to change the click configuration in ROUTER1. For doing this, I 
> have a separate application which connects to port 13000 on ROUTER1 and 
> invokes the relevant controlsocket server commands (writedata and write on 
> hotconfig handler). The server returns a success i.e, 200 OK indicating 
> that the new config has been applied correctly. However, when I try to ping 
> PC2   from PC1 it starts failing.

Note that every time any of the XORP interfaces is reconfigured
XORP will regenerate new Click configuration using
user-click-config-generator-file, and that configuration will
overwrite your config. Hence, make sure that if you do hotswap by
directly writing to port 13000, the user-click-config-generator-file
is updated as well to contain your new changes.
Though, if you don't change anything in the XORP configuration while
playing with the hotswap, then this shouldn't have impact on your
results. 

> I have compared the old and new click configuration and there is nothing 
> which should prevent the ping from failing (I have changed a few parameters 
> to my custom/local click elements). Is there something fundamentally 
> incorrect with the above approach.

One thing to check is the Click forwarding table. For that purpose
you need to talk directly to the Click forwarding element, because
from the XORP CLI you can print only the routing entries that are
stored inside XORP.
Off the top of my head:

telnet localhost 13000
READ _xorp_rt4::table

Do this before and after the hotswap.

My guess is that the hotswap has cleared the forwarding entries
in ROUTER1, including the entry necessary to reach PC2.

If the forwarding entries are fine, then you could try to test the
hotswap without XORP. For that purpose you need to do the following
on ROUTER1:

1. Start XORP and make sure the forwarding is running
2. Read the Click configuration as installed by XORP and save it to
   a file.
3. Stop XORP and start Click by hand using the above saved
   configuration.
4. Perform the hotswap and see what happens.
   If the forwarding fails as before, then you need to track the
   problem in the Click level. If the hotswap succeeds, then the
   problem is somewhere in XORP.

Regards,
Pavlin

> I have also tried defining my own controlsocket (port 14000) via config 
> file (added a statement in /usr/localxorp/fea/xorp_fea_click_config inorder 
> to do this). But I encounter the same issue. The server returns OK after 
> each hotswap attempt and the ping fails.
> 
> Would be great if I get some tips on fixing the above issue. Please let me 
> know if I have missed out anything which would help in this investigation.
> 
> Additionally after hotswap, a tcpdump on eth3 (Router1) indicates that the 
> ping packets are not reaching eth3, I can see it on eth4. The xorp routing 
> table is also fine.
> 
> Thanks
> Swati
> 
> 
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