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Configuring Multi-chassis Link Aggregation
MC-LAG prevents MAC
on the L
aggregate even though the original ARP request packet was actually received through the VFL.
A
The MAC addresses learned on MC-LAG ports in one switch are learned on the same MC-LAG ports on
the peer switch.
4
Step 4: ARP Reply
•
Switches M
and M
1
an IP address of any of either of their IP interfaces.
•
Eventually, the ARP request will reach the destination host B, which will respond to the ARP request
as indicated below.
MAC Table
⇒ L
MAC
A
A
⇒ L
MAC
B
B
PC
The ARP reply is a unicast packet as follows.
•
Source MAC = MAC
•
Destination MAC = MAC
5
Step 5: MAC
Learning
B
As the ARP reply packet traverses the system on its way back via the path Host B ==> S
=> Host A, the MAC
6
Step 6: Regular Traffic Flow
The packet eventually reaches the Host A. From this moment on, Host A will be able to communicate with
Host B using IP over the Layer 2 multi-path infrastructure provided by the MC-LAG aggregates.
Key Points
•
The MC-LAG peers perform only Layer 2 switching and learning operations despite the fact that actual
traffic flowing between the hosts is IP-based.
•
MAC addresses learned on an MC-LAG aggregate on one of the MC-LAG peers are also learned on
the other peer on the same MC-LAG aggregate.
OmniSwitch AOS Release 7 Network Configuration Guide
from being learned on the VFL ports of switch M
A
do not respond to the ARP request because the destination IP address (IP
2
M
1
L
A 1
L
A 2
MC-LAG-A
S
1
ARP Reply Over MC-LAG
B
A
address is learned by the M
B
M
2
L
B2
L
B1
MC-LAG-B
S
ARP Reply
2
switch on the aggregate L
1
March 2011
MC-LAG Packet Flow
but shows MAC
as learned
2
A
) is not
B
MAC Table
⇒ L
MAC
A
A
Host B
(MAC
, IP
)
B
B
PC
==> M
=> S
2
1
.
B
page 8-19
1
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