Frame relay: Multilink point to point frame relay

Reference: http://www.cisco.com/en/US/docs/ios/12_2s/feature/guide/fs_mfr.html

Multilink Frame Relay (FRF.16.1)

1. This technology aggregates multiple number of physical serial interfaces into one bundle.

a. This provides link redundancy i.e. if a physical link of a bundle has failed, the frame relay link will still be available.

b. This also provides bandwidth aggregation from multiple serial interfaces. (See http://www.cisco.com/en/US/docs/ios/12_2s/feature/guide/fs_mfr.html#wp1054102)

2. The aggregated interfaces is known as bundle. The interfaces within the bundle are known as bundle links.

3. MFR bandwidth classes:

Class A (single link) – Bundle is up when at least one bundle link is up, if all bundle links is down the bundle is down. This is the default class if no bandwidth class is specified.

Class B (All links) – Bundle is up as long as all bundle links is up, if one bundle link is down the bundle is down.

Class C (Threshold) – The bundle is up as long as the minimum number of bundle links is up, if the minimum number of online bundle links is not met the bundle is down.

Demonstration

R1 is the frame relay switch. R2 has two serial links which are bundled.

R2 configuration

interface MFR1
 no ip address
end
interface MFR1.1 point-to-point
 ip address 192.168.1.2 255.255.255.0
 frame-relay interface-dlci 213
end
interface Serial0/0
 no ip address
 encapsulation frame-relay MFR1
 no arp frame-relay
 frame-relay multilink lid link1
end
interface Serial0/1
 no ip address
 encapsulation frame-relay MFR1
 no arp frame-relay
 frame-relay multilink lid link2
end

Under the serial interface there is this command frame-relay multilink lid command. This command simply names the bundle link.

You can specify bid to interface mfR by using <code>frame-relay multilink bid</code>

R2(config)#int mfR 1
R2(config-if)#frame-relay multilink bid r2
R2(config-if)#

You can explicitly configure the bandwidth class by using <code>frame-relay multilink bandwidth-class a|b|c</code> but this option is not available on my IOS.

R2 show frame-relay map

R2#sh frame-relay map
MFR1.1 (up): point-to-point dlci, dlci 213(0xD5,0x3450), broadcast
          status defined, active
R2#

Reference: http://www.cisco.com/en/US/docs/ios/12_2s/feature/guide/fs_mfr.html#wp1054143

Point to point

1. Point to point sub interface only terminates one PVC.

2. Does not require layer3 to layer2 resolution since there is only one PVC.

3. Does not require inverse arp, but still responds to inverse arp enquiry.

R3 configuration

interface Serial0/0
no ip address
encapsulation frame-relay
end

interface Serial0/0.312 point-to-point
ip address 192.168.1.3 255.255.255.0
frame-relay interface-dlci 312
end

R3 show frame-relay map

R3#sh frame-relay map
Serial0/0.312 (up): point-to-point dlci, dlci 312(0x138,0x4C80), broadcast
          status defined, active
R3#

Shutdown R2 interface

R2(config)#int se0/0
R2(config-if)#shut
R2(config-if)#
*Mar  1 01:11:56.291: %LINK-5-CHANGED: Interface Serial0/0, changed state to administratively down
*Mar  1 01:11:57.293: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to down
R2(config-if)#

But R3 is still reachable.

R2#ping 192.168.1.3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 44/81/141 ms
R2#

The frame-relay link is still up.

R2#sh frame-relay map
MFR1.1 (up): point-to-point dlci, dlci 213(0xD5,0x3450), broadcast
          status defined, active
R2#
R3#sh frame-relay map
Serial0/0.312 (up): point-to-point dlci, dlci 312(0x138,0x4C80), broadcast
          status defined, active
R3#
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