Alaerte,
I can think of a couple ways to doing this. Be forewarned. Both are ugly.
Method #1: Relocate the servers /30 subnet
------------------------------------------
We'll say the server's IP address is 192.3.3.254/24. Create a secondary
IP address on R2 for 192.3.3.252/30. R2's secondary address becomes
192.3.3.253/30, the server can stay 192.3.3.254/24. Make sure that R3
knows how to reach the 192.3.3.252/30 subnet (either static route or a
classless routing protocol).
How it works:
Proxy ARP. Stations on VLAN 300 attempting to connect to the server will
ARP for 192.3.3.254, for which R3 has a "better route", and will respond
to the ARP with its own MAC. Traffic to 192.3.3.254 will be routed to
R2. The reverse will happen when 192.3.3.254 attempts to respond to the
client, it ARPs, R2 knows of a route and responds with its MAC, the
packet is routed back.
Other info:
- I've assumed that the server address was 192.3.3.254, it could have
been anything. The /30 subnet would change accordingly.
- I've assumed that .252 and .253 were not already in use. If they were,
connectivity to these stations would be broken. You can get around this
problem by configuring (and redistributing) static routes for
192.3.3.252/32 and 192.3.3.253/32 pointed back towards Vlan 300 on R3.
- L2 Broadcasts will not be available to/from the new server
Method #2: Virtual router
-------------------------
This method has the unique property of being both cleaner (from a caveat
perspective) and uglier at the same time. Imagine walking into this at a
customer site -- how long would it take you to figure out what was going
on? :)
Once again we'll say the server's IP address is 192.3.3.254/24.
Configure a static route on R3 as follows:
ip route 192.168.3.254 255.255.255.255 (ip_of_R2)
On R2, determine an IP address that isn't used for use as a virtual
router. We'll say 192.168.2.254/24 isn't used. Create a static route on
R2 to the server through the virtual router:
ip route 192.168.3.254 255.255.255.255 192.168.2.254
The virtual gateway doesn't exist so pings to it will fail. Don't worry
about that yet. Move the server to VLAN 200 without changing its IP
address or mask. Determine the MAC address of the server. We'll say
0001.0002.0003. On R2, configure the MAC for the virtual router to be
the server's IP:
arp 192.168.2.254 0001.0002.0003 arpa
You must perform similar steps on the server. We'll assume that its
default gateway has not changed. We'll also assume that its default
gateway was 192.3.3.1. Configure a static ARP entry for the default
gateway that reflects R2's Ethernet MAC (0102.0304.0506):
arp -s 172.30.16.254 01:02:03:04:05:06
Make sure that R3 knows how to reach the 192.3.3.254/32 subnet (either
add a static route or redistribute on R2).
How it works:
Vlan 300 stations broadcast ARP, and R3 responds with its MAC (Proxy
ARP). R3 forwards the packets to R2. R2 forwards the packets directly to
the server (although it believes it is forwarding to another gateway).
The server receives the packet because the MAC was correct, notices that
it is the end station, and processes the packet. Traffic from the server
to VLAN 300 is possible using Proxy ARP as describe in Method 1. Traffic
to/from other VLANs (VLAN 100) will also work fine since the server
forwards all of its "default gateway" traffic to the correct default
gateway, R2.
Other info:
- I've assumed that the server address was 192.3.3.254, it could have
been anything.
- The only 192.3.3.0/24 address used on VLAN 200 (other than the servers
IP) is the Ethernet IP address of R3.
- L2 Broadcasts will not be available to/from the new server
- Pings to the virtual router will fail (it /is/ virtual after all),
even though the server will have full network connectivity.
If you get around to actually doing either of these in the lab and run
into trouble, let me know (the above was written from memory, and I may
have missed a step or two). I originally came across these ideas after
reading Doyle and configured them in the lab just to see if I could pull
it off. Yep. :)
You would be surprised with some of the crazy labs you can make for
yourself when IP addresses don't need to be contiguous or need to match
the local router!
- Tom
alaerte Vidali wrote:
> Need to transport multiple Vlans over PoS.
>
> Any Thoughts?
>
> It is a short term need. It is necessary to move a server without changing
> its IP address from Vlan 300 to Vlan 200 and a server from Vlan 100 to Vlan
> 200.
>
>
> Vlan 100 (192.1.1.0) R1 ----------- R2 (192.2.2.0) Vlan 200
> | |
> | |
> Vlan 300 (192.3.3.0) R3---------------
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