Frame Relay Notes - CCIE

1. A point-to-point sub interface can only accommodate a single DLCI at any given time. Point-to-point sub-interfaces are treated by the IOS like a physical point-to-point interface and do not need either inverse-arp or frame-relay map statements.
2. Multipoint DLCI’s rely on either inverse-arp or frame-relay map statements for proper operation.
3. You must manually clear inverse-arp with a clear frame-inarp command to remove any undesired inverse-arp entries.
4. The broadcast parameter is required for protocols such as OSPF
5. If the router is reloaded inverse-arp will be disabled for any DLCI that is used with a frame-relay map statement.
6. As a rule when configuring frame-relay map statements make note of the protocol and the DLCI specified if there are any inverse mappings for that same protocol referencing the same DLCI replace the inverse-arp entries with frame-relay map statements.
7. Rules to remember when configuring point-to-point sub-interfaces are:
• No frame-relay map statements can be used with point-to-point sub-interfaces
• One and only once DLCI can be associated with a single point-to-point interfaces
8. Without the frame-relay interface DLCI command, all DLCI’s are assigned to the physical Interface Split horizon only blocks routing updates in a hub and spoke topology
9. A Cisco IOS remedy to this split horizon problem is to disable split horizon on the hub router in a frame-relay network this can be performed at the interface configuration mode.
10. Split horizon is disabled on frame-relay physical IP interfaces split horizon is enabled on framerelay point-to-point and multi-point IP sub-interfaces.
11. OSPF is not affected by the rule of split horizon since it does not apply it.
12. A remedy to the problem of “hello mismatches” is using the Cisco IOS interface configuration command “IP OSPF network”:
13. A popular selection for OSPF networks is the point-to-multipoint option.
14. When using only physical interfaces in a hub and spoke topology you need to add a frame-relay map statement on the spoke routers to assure spoke to spoke reachability nothing needs to be done to the hub router.
15. If using point-to-point sub-interfaces each sub-interface must be configured as a separate sub net. If a physical or multipoint sub interface is being used at the hub remember to disable split horizon at the hub