KB.15.15

Figure 66 ISC link failure with peer-keepalive

Peer-keepalive messages are sent by both the DT switches as soon as the switches detect that the

ISC link is down. Peer-keepalive message transmission (sending and receiving) is suspended until

the peer-keepalive hold timer expires. When the hold timer expires, the DT switches begin sending

peer-keepalive messages periodically while receiving peer-keepalive messages from the peer

switch. If the DT switch fails to receive any peer-keepalive messages for the timeout period, it

continues to forward traffic, assuming that the DT peer switch has completely failed.

Conversely, if the failure is because the ISC link went down and the secondary DT switch receives

even one peer-keepalive message from the primary peer, the secondary switch disables all its DT

ports. The primary switch always forwards the traffic on its DT ports even if it receives peer-keepalive

messages from the secondary DT switch.

In both situations, if the ISC link or the DT switch becomes operational, both the DT peers sync the

MAC addresses learned during the failover and continue to forward traffic normally. The

peer-keepalive timers and operation is halted.

Maximum DT trunks and links supported

Table 14 (page 163) shows the maximum number of DT trunks and DT links that are supported.

Table 14 Maximum supported DT trunks and links

Max numberDescription

144Maximum number of groups (DT trunks) in a DT switch (that is, maximum number of servers

supported)

2Maximum number of switches that can be aggregated

4Maximum number of physical links that can be aggregated in a single switch from a server

(that is, maximum number of ports that can be in a trunk connected to a single switch)

From the server perspective, this means that there could be a maximum total of 60 servers connected

to two DT switches. Each server can have up to four physical links aggregated in a single switch,

meaning that a single server could have a maximum of eight links (that is, four on each DT switch)

in a DT trunk.

About configuring peer-keepalive links 163