5-12Configuring SA Message CacheWith the SA message caching mechanism enabled on the router, the group that a new membersubsequently joins can obtain all active sources directly from the SA cache and join the correspondingSPT source tree, instead of waiting for the next SA message.You can configure the number of SA entries cached in each MSDP peer on the router by executing thefollowing command, but the number must be within the system limit. To protect a router against Denialof Service (DoS) attacks, you can manually configure the maximum number of SA messages cached onthe router. Generally, the configured number of SA messages cached should be less than the systemlimit.Follow these steps to configure SA message cache:To do... Use the command... RemarksEnter system view system-view —Enter MSDP view msdp —Enable SA message cachingmechanism cache-sa-enable OptionalEnabled by defaultConfigure the maximum number ofSA messages that can be cachedpeer peer-addresssa-cache-maximum sa-limitOptionalThe default is 2,048.Configuring the Transmission and Filtering of SA Request MessagesAfter you enable the sending of SA request messages, when a router receives a Join message, it sendsan SA request message to the specified remote MSDP peer, which responds with an SA message thatit has cached. After sending an SA request message, the router will get immediately a response from allactive multicast sources. The SA message that the remote MSDP peer sends in response is cached inadvance; therefore, you must enable the SA message caching mechanism in advance. Typically, onlythe routers caching SA messages can respond to SA request messages.After you have configured a rule for filtering received SA messages, if no ACL is specified, all SArequest messages sent by the corresponding MSDP peer will be ignored; if an ACL is specified, the SArequest messages that satisfy the ACL rule are received while others are ignored.Follow these steps to configure the transmission and filtering of SA request messages:To do... Use the command... RemarksEnter system view system-view —Enter MSDP view msdp —Enable SA message cachingmechanism cache-sa-enableOptionalBy default, the router caches the SAstate upon receipt of an SA message.Enable MSDP peers to send SArequest messagespeer peer-addressrequest-sa-enableOptionalBy default, upon receipt of a Joinmessage, the router sends no SArequest message to its MSDP peer butwaits for the next SA message.
