H3C Technologies H3C S7500E Series Switches - Manual (Page 216)

7-15
z Upon receiving an SA message with an encapsulated multicast data packet, the router
decrements the TTL value of the multicast packet by 1 and then checks the TTL value. If the TTL
value is less than the threshold, the router does not forward the SA message to the designated
MSDP peer; if the TTL value is greater than or equal to the threshold, the router re-encapsulates
the multicast data in an SA message and sends the SA message out.
Follow these steps to configure a filtering rule for receiving or forwarding SA messages:
To do... Use the command... Remarks
Enter system view system-view —
Enter public instance MSDP view
or VPN instance MSDP view
msdp [ vpn-instance
vpn-instance-name ]
—
Configure an SA message creation
rule
import-source [ acl acl-number ]
Required
No restrictions on (S, G) entries by
default
Configure a filtering rule for
receiving or forwarding SA
messages
peer peer-address sa-policy
{ import | export } [ acl
acl-number ]
Required
No filtering rule by default
Configure the TTL threshold for
multicast data packet
encapsulation in SA messages
peer peer-address minimum-ttl
ttl-value
Optional
0 by default
Configuring the SA Cache Mechanism
To reduce the time spent in obtaining the multicast information, you can enable the SA cache
mechanism to cache (S, G) entries contained in SA messages locally on the router. However, the
more (S, G) entries are cached, the larger memory space of the router is used.
With the SA cache mechanism enabled, when receiving a new (*, G) join message, the router
searches its SA cache first:
z If the corresponding (S, G) entry does not exist in the cache, the router waits for the SA message
its MSDP peer will send in the next cycle;
z If the corresponding (S, G) entry exists in the cache, the router joins the corresponding SPT
rooted at S.
To protect the router effectively against denial of service (DoS) attacks, you can set a limit on the
number of (S, G) entries the router can cache.
Follow these steps to configure the SA message cache:
To do... Use the command... Remarks
Enter system view system-view —
Enter public instance MSDP view or VPN
instance MSDP view
msdp [ vpn-instance
vpn-instance-name ]
—