Would it be possible for SB to produce a diagram and/or a worked example or two that illustrates how the IP/Mac "pair" changes as a packet travels from a client's computer out to the Internet and back via a number of SB units (ABs and APPOs)?
We are frequently having to swap IP addresses if clients "mess around" with different computers into an AB and the arp table somewhere gets confused (also happens if/when we are testing with our own computer at a customer site), and I would like to understand much better exactly what happens.
When the aB (in multimac mode) receives a packet from the ethernet side it stores the source MAC and source IP of the packet in a table.
Packet on ethernet wire between ClientPC and aB: SMAC=clientMAC SIP=clientIP DMAC=destMAC DIP=destIP
It then replaces the source MAC with its own MAC, and forwards the packet to the wireless side. The AP receives the packet and forwards it on the ethernet side.
Packet on ethernet wire behind the AP: SMAC=aBMAC SIP=ClientIP DMAC=destMAC DIP=destIP
Now we send a packet in the opposite direction.
Packet on ethernet wire behind the AP: SMAC=senderMAC SIP=senderIP DMAC=aBMAC DIP=clientIP
When the aB (in multimac mode) receives a packet from the wireless side it looks at the destination IP and looks for a matching IP/MAC in its table. It then replaces the destination MAC with the MAC in the table and forwards it to the ethernet side.
Packet on ethernet wire between clientPC and aB: SMAC=senderMAC SIP=senderIP DMAC=clientMAC DIP=clientIP
From the point of view of the client PC, it is talking directly to the
router or whatever is on the other side of the wireless link. From the
point of view of the router in your NOC, it is talking to a device which has the MAC address of the airBridge and the IP address of the client.
I think the aB also changes ARP reply packets received from its ethernet side (replaces the Sender MAC Address field in the packet with its own MAC). Never bothered tracing it, though, since I'm only interested in running PPPoE over the aB. ;)
-- LarsG
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