Re: arp table - same mac address shows two ip addresses

[Grant Taylor <gtaylor@xxxxxxxxxxxxxxxxxx>]

On 10/18/2018 10:45 AM, Grant Taylor wrote:
> My intention is to create the following configuration using network 
> namespaces:
>
> (A)---1---(B)---2---(C)
>
> Where A, B, and C are the test network namespaces and 1 and 2 are vEth 
> pairs between them.
>
> I was originally going to start with one test, see if A could 
> communicate with B via 2.B.

I can get ARP to respond.  But I've not gotten ICMP to function yet.  It 
looks like it may be, funny enough, an ARP issue.  B has two ARP entries 
for A's IP, one from the what it learned from A's ARP request and an 
incomplete entry.  I've not done any more investigation to see if I can 
make this work.  Yet.  }:-)

> After your earlier email about hosts moving from one physical network to 
> another, I'm going to see if 1 can be configured with 2.A and 
> communicate with 2.B via the 1 network.

I think I'm going to need to reconfigure the network a bit to have B 
function as a router with A being on the wrong interface.  Probably 
something like this:

(A)---1---(B)---2---(C)
           |
           3
           |
          (D)

Such that A looks like it moved from the 3 network to the 1 network. 
With C being something on the other side of "the router", B.

> I'll share the commands I use to create the lab topology and subsequent 
> commands to test.

Here are the commands that I used:

ip netns add a
ip netns add b
ip netns add c
ip link add name a type veth peer name b
ip link set dev a netns b
ip link set dev b netns a
ip link add name b type veth peer name c
ip link set dev b netns c
ip link set dev c netns b

ip netns exec a ip link set dev b up
ip netns exec b ip link set dev a up
ip netns exec b ip link set dev c up
ip netns exec c ip link set dev b up
ip netns exec a ip addr add 192.0.2.1/24 dev b
ip netns exec b ip addr add 192.0.2.2/24 dev a
ip netns exec b ip addr add 198.51.100.2/24 dev c
ip netns exec c ip addr add 198.51.100.3/24 dev b
ip netns exec a ip addr add 198.51.100.1/24 dev b

Note:  These commands are a reconstruction for others, I actually have 
aliases and scripts that do much of this behind the scenes for me.  Let 
me know if you can't reproduce something.

Initially, B wouldn't respond to ARP requests from A for 198.51.100.2 
when I tried to ping it.  I found that I had to reset rp_filter to it's 
default value of 0.  —  I keep rp_filter set to 1 on my machines.

Once I had the network namespace TCP/IP stacks set to defaults, B did in 
fact respond to A's ARP request for an IP on the 2nd network.

I've not done any testing beyond that yet.



--
Grant. . . .
unix || die

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