Bug 271168 - [carp] Packets send to carp gateway are forwarded to all ECMP routes
Summary: [carp] Packets send to carp gateway are forwarded to all ECMP routes
Status: Closed Not A Bug
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: CURRENT
Hardware: Any Any
: --- Affects Only Me
Assignee: freebsd-net (Nobody)
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2023-05-01 13:57 UTC by Arnaud HOUDELETTE
Modified: 2023-05-01 15:57 UTC (History)
3 users (show)

See Also:

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Description Arnaud HOUDELETTE 2023-05-01 13:57:39 UTC 

    


    


      



        
          Comment 1
        

        
          Arnaud HOUDELETTE

        

        
        

        
          2023-05-01 14:05:51 UTC
        

      






Considering this scenario : 

              +--------------------------+
              |                          |
+--------+    |        FreeBSD           |
| Host 1 +----+ifAdm   router box        |
+--------+    |carp                      |
              |                          |
              |   vl10             vl11  |
              +-----+---------------+----+
                    |               |
                 +--+---+        +--+---+
                 | RT-A |        | RT-B |
                 +--+---+        +---+--+
                    |                |
                  --+---------+------+----
                              |
                          +---+----+
                          | Host 2 |
                          +--------+


Carp ifAdm IP is default gateway for Host 1
The router box as two routes to Host 2 network (ECMP), via RT-A and RT-B

Packets send by Host 1 to Host 2 are received twice (via RT-A and RT-B).

carp if is configured as follow : 

ifconfig_ifAdm="169.254.1.1/24"
ifconfig_ifAdm_alias0="inet vhid 1 pass testpass alias 195.220.135.193/26"

removing carp on interface does not show the issue :
ifconfig_ifAdm_alias0="inet alias 195.220.135.193/26"

    


    


      



        
          Comment 2
        

        
          Alexander V. Chernikov

        

        
            freebsd_committer
            freebsd_triage
        

        
          2023-05-01 15:05:12 UTC
        

      






Could you share ifconfig, netstat -4rnW and, most importantly, the tcpdump -lnvvs0 output from both vl10 and vl11 interfaces?

    


    


      



        
          Comment 3
        

        
          Arnaud HOUDELETTE

        

        
        

        
          2023-05-01 15:57:46 UTC
        

      






After more investigation on the issue, it appears that the culprit was the second carp router which deconfigured carp interface continued to process packets to the carp MAC address.

Will submit another PR if (and only if) I manage to reproduce on a virtual environment.