[nycbug-talk] FreeBSD Dual homed

[Rodrique Heron]

Brian A. Seklecki wrote:
>
> Okay dual verizon adsl lines.  A common question.
>
> I'm assuming that you're trying to serve certain services off-of 
> 150.210.240/24 and wondering why packets from 3rd party nework sources 
> get there but not reply.
The service in question is SSH, as you can see from my netstat output:

root     sshd       609   4  tcp4   *:22                  *:*

It's listening on all available interface, so I should be able to 
connect from 150.210.240/24 or /150.210.160/24. I don't seem to have 
this problem when one interface is configured on a private address 
space. i.e. 192.168.2.0/24.



>
> There can only be one default gateway.  The gateway selection decision 
> is not based on any type of "state" table (by default), so:
>
> 1) A packet received on em0 with a foreign network source address and 
> a destination address of 150.210.240.x/32 will be received, 
> decapsulated, processed by the kernel -- the reply packet will be 
> generated and transmitted out of em1 with a source address of 
> 150.210.160.xxx/32 and a destination of [foreign].
>
> Its just the nature of the TCP/IP stack and "standard" routing.
>
> I've seen discussion on misc at openbsd.org on a pf(4) feature that 
> somehow works around this.
>
> ~BAS
>
>
>> Internet:
>>
>> Destination        Gateway            Flags    Refs      Use  Netif 
>> Expire
>>
>> default            150.210.160.254    UGS         0      415    em1
>>
>> 150.210.160/24     link#2             UC          0        0    em1
>>
>> 150.210.240/24     link#1             UC          0        0    em0
>>
>> 150.210.240.32     00:0c:29:62:78:63  UHLW        1        6    
>> em0    547