H3C Technologies H3C S12500 Series Switches - Manual (Page 213)

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By configuring a filtering rule for receiving or forwarding SA messages, you can enable the switch to filter
the (S, G) forwarding entries to be advertised when receiving or forwarding an SA message, so that the
propagation of multicast source information is controlled at SA message reception or forwarding.
By configuring a TTL threshold for multicast data packet encapsulation in SA messages, you can control
the multicast data packet encapsulation in SA messages and limit the propagation range of SA
messages:
• Before creating an SA message with an encapsulated multicast data packet, the switch checks the
TTL value of the multicast data packet. If the TTL value is less than the threshold, the switch does not
create an SA message. If the TTL value is greater than or equal to the threshold, the switch
encapsulates the multicast data in an SA message and sends the SA message.
• After receiving an SA message with an encapsulated multicast data packet, the switch 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 switch does not forward the SA message to the designated MSDP peer. If the TTL
value is greater than or equal to the threshold, the switch re-encapsulates the multicast data in an
SA message and sends the SA message.
To configure a filtering rule for receiving or forwarding SA messages:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter public network MSDP
view or VPN instance MSDP
view.
msdp [ vpn-instance
vpn-instance-name ]
N/A
3. Configure an SA message
creation rule.
import-source [ acl acl-number ]
No restrictions on (S, G) entries by
default.
4. Configure a filtering rule for
receiving or forwarding SA
messages.
peer peer-address sa-policy
{ import | export } [ acl
acl-number ]
No filtering rule by default.
5. 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 switch. However, caching (S, G) entries
uses memory space on the switch.
When the SA cache mechanism is enabled and the switch receives a new (*, G) join message, the switch
searches its SA cache first.
• If the corresponding (S, G) entry does not exist in the cache, the switch waits for the SA message
that its MSDP peer will send in the next cycle.
• If the corresponding (S, G) entry exists in the cache, the switch joins the corresponding SPT rooted
at S.
To protect the switch against denial of service (DoS) attacks, you can set a limit on the number of (S, G)
entries the switch can cache.
To configure the SA message cache: