CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- Frame Relay Multipoint Subinterface configuration on RT4:
!
interface Serial0/0
encapsulation frame-relay
!
interface Serial0/0.888 multipoint
ip address 200.1.3.2 255.255.255.0
frame-relay interface-dlci 101
frame-relay interface-dlci 105
!
interface FastEthernet1/0
ip address 172.16.4.1 255.255.255.0
- Frame Relay Multipoint Subinterface configuration on RT5:
!
interface Serial0/0
encapsulation frame-relay
!
interface Serial0/0.888 multipoint
ip address 200.1.3.3 255.255.255.0
frame-relay interface-dlci 101
frame-relay interface-dlci 104
!
interface FastEthernet1/0
ip address 172.16.5.1 255.255.255.0
- A multipoint subinterface is used when multiple VCs are associated with a subinterface.
- No mapping configuration is required, as Inverse ARP is enabled by default on multipoint
subinterfaces; while point-to-point subinterfaces never require mapping configuration.
- The output of the show frame-relay map EXEC command on RT1 includes the L3 address
mapping information on multipoint subinterfaces (learnt via Inverse ARP):
RT1#sh frame-relay map
Serial0/0.102 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast
status defined, active
Serial0/0.103 (up): point-to-point dlci, dlci 103(0x67,0x1870), broadcast
status defined, active
Serial0/0.888 (up): ip 200.1.3.2 dlci 104(0x68,0x1880), dynamic,
broadcast,, status defined, active
Serial0/0.888 (up): ip 200.1.3.3 dlci 105(0x69,0x1890), dynamic,
broadcast,, status defined, active
- The disadvantage of Inverse ARP is whenever the PVC data link layer is up, a DTE router needs
to learn the status and DLCIs of VCs and waits for the Inverse ARP process to occur, which can
take a considerable amount of time! Whereas with manually resolved PVCs, data transmission
is allowed as soon as the data link layer is up. Routers send InARP Request packets every 1 min.
A remote router that receives the InARP Request packet would reply with an InARP Reply
packet. Eventually both routers would have the L3-to-L2 address mapping to reach each other.
- The no interface {subif-num} global configuration command is insufficient to remove a
subinterface. The subinterface will still exist in the router’s memory. A router reboot is required.
This also applied when changing the subinterface type (reboot is required).
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com