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Cisco WAN Manager User’s Guide
Version 10.5, Part Number 78-12945-01 Rev. D0, August 2003
Appendix A Internet Connectivity
SVC Connections
specifies which SVC on the router should be used. The ATM interface on the router, if using LLC
encapsulation as described in RFC1483, prefixes the data with a header that specifies to the remote end
of the SVC that the data is encapsulated IP data. The router then transmits the data onto the SVC.
The encapsulated IP data is received by the MGX 8850 Release 2 IPATM interface on one of its router
SVCs. Using RFC1483 if the data is on an SVC supporting LLC encapsulation, IPATM interface strips
off the prefixed header and verifies that the data is truly IP data. If it is, the IPATM interface performs a
very important function: it adds an entry to a local cache to remember which SVC was used by the IP
host/workstation to reach the MGX 8850 Release 2. The cache has the following format:
• IP Address of IP host/workstation
• SVC VC identifier that data was received on
• Timer to be used to time-out the cache entry for the IP host/workstation
Should the cache entry already exist for the IP host/workstation it is updated if the SVC being used has
changed. This allows the IPATM interface to dynamically choose the correct SVC necessary. After
setting up the cache entry, IPATM interface then adds a new VxWorks IP host-route for the IP
host/workstation. The IP host-route will allow VxWorks IP stack to give all IP data that is to be sent to
the IP host/workstation to the IPATM interface. Once the IP host-route is set up, the IPATM interface
gives the received IP data to VxWorks IP layer. From there, it will be routed to the appropriate server
application of the MGX 8850 Release 2.
Should the server application of the MGX 8850 Release 2 need to respond to the data received from the
IP host/workstation, it will do so by making a client/server API call to VxWorks. The data from the
server will eventually reach the VxWorks IP layer, where a IP route table will be searched to determine
the correct interface that should be used for the transmission. The VxWorks IP layer will find the IP
host-route that was previously added by the IPATM interface when the data was originally received and
the data will be given to IPATM.
The IPATM interface, when given IP data from VxWorks IP layer, will perform a cache lookup of the
destination IP address of the data. In the cache, an entry should exist that specifies which SVC VC
identifier should be used for sending the IP data. If found, the data is prefixed with a header as described
by RFC1483 if the SVC supports LLC encapsulation and sent. If not, the data is dropped and a statistic
is kept for the dropped data.
The router will receive the data transmitted by the IPATM interface, strip the RFC1483 header if
required, and transmit the data to the correct IP interface for reaching the IP host/workstation. Again,
this will be accomplished using a IP route table lookup in the router.
The IP host/workstation will receive the data transmitted by the MGX 8850 Release 2 server and forward
the data to the appropriate TCP/IP client running on the host/workstation.
SVC Connections
To configure the type of network as shown in Figure A-1, you must first create an SVC connection
between an MGX 8850 Release 2 node (MGX 8850 C) and a router (CWM RTR-1). Configure the
connection to MGX 8850 C as your CWM gateway. Next, configure SVC connections between the CWM
router and each of the other MGX 8850s.
The following two sections provide information about ample configurations and the features they offer.