IS-IS Bandwidth Based Metrics

Full Configs

• pe1.cfg
• pe2.cfg

Login details are: admin/admin

IS-IS key is: admin

This was tested using cEOS version 4.31.2F.

 

Topology

PE1 and PE2 have two port-channels between them. Port-Channel1 has a single member link (1Gbps), Port-Channel2 has two members links (10Gbps + 1Gbps).

IS-IS is configured using a reference bandwidth of 100Tbps.

 

Higher Bandwidth Preferred

Traffic between PE loopback IPs uses the Po2 <-> Po2 link due to the higher bandwidth resulting in a lower IS-IS metric (which is more preferred). This happens because the Po2 interface speed (11Gbps) is closer to the reference bandwidth (100Tbps) than the Po1 interface speed (1Gbps).

pe1#show interfaces status 
Port       Name       Status       Vlan     Duplex Speed  Type            Flags Encapsulation
Et1        et1 -> et1 connected    in Po1   full   1G     EbraTestPhyPort                   
Et2        et2 -> et2 connected    in Po2   full   1G     EbraTestPhyPort                   
Et3        et3 -> et3 connected    in Po2   full   10G    EbraTestPhyPort                   
Ma0                   connected    routed   a-full a-1G   10/100/1000                       
Po1        po1 -> po1 connected    routed   full   1G     N/A                               
Po2        po2 -> po2 connected    routed   full   11G    N/A                               


pe1#show isis interface brief 

IS-IS Instance: Gandalf VRF: default

Interface     Level IPv4 Metric IPv6 Metric Type           Adjacency
------------- ----- ----------- ----------- -------------- ---------
Loopback0     L2             10          10 loopback       (passive)
Port-Channel1 L2         100000      100000 point-to-point         1
Port-Channel2 L2           9090        9090 point-to-point         1

pe1#show ip route 10.0.0.2/32 | beg 10.0.0.2
 I L2     10.0.0.2/32
           directly connected, Port-Channel2

 

Bandwidth Is Dynamic

It can be seen that if the 1G link is removed from Po2, it's bandwidth changes from 11Gbps to 10Gbps and the IS-IS metric updates automatically to match this:

pe1#conf t
pe1(config)#int et2
pe1(config-if-Et2)#shut
Dec  6 11:51:24 pe1 Ebra: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet2 (et2 -> et2), changed state to down
Dec  6 11:51:24 pe1 Lag: %LAG-5-MEMBER_REMOVED: Interface Ethernet2 (et2 -> et2) has left Port-Channel2 (po2 -> po2) due to: unknown reason
pe1#show int po2
Port-Channel2 is up, line protocol is up (connected)
  Hardware is Port-Channel, address is 001c.7335.07ea
  Description: po2 -> po2
  Internet address is unnumbered. 10.0.0.1/32 borrowed from Lo0
  Broadcast address is 255.255.255.255
  IP MTU 1500 bytes (default), BW 10000000 kbit
  Full-duplex, 10Gb/s 
  Active members in this channel: 1
  ... Ethernet3 , Full-duplex, 10Gb/s
  Fallback mode is: off
  Up 39 minutes, 39 seconds
  2 link status changes since last clear
  Last clearing of "show interface" counters never
  5 minutes input rate 1.43 kbps (0.0% with framing overhead), 0 packets/sec
  5 minutes output rate 9 bps (0.0% with framing overhead), 0 packets/sec
     454 packets input, 248566 bytes
     Received 1 broadcasts, 452 multicast
     0 input errors, 0 input discards
     174 packets output, 198565 bytes
     Sent 1 broadcasts, 172 multicast
     0 output errors, 0 output discards


pe1#show isis interface brief 

IS-IS Instance: Gandalf VRF: default

Interface     Level IPv4 Metric IPv6 Metric Type           Adjacency
------------- ----- ----------- ----------- -------------- ---------
Loopback0     L2             10          10 loopback       (passive)
Port-Channel1 L2         100000      100000 point-to-point         1
Port-Channel2 L2          10000       10000 point-to-point         1


pe1#show ip route 10.0.0.2/32 | beg 10.0.0.2
 I L2     10.0.0.2/32
           directly connected, Port-Channel2

 

Port-Channel Minimum Bandwidth

Re-adding the 1G link to Po2 and removing the 10G link drops it below the minimum required bandwidth for this Port-Channel to stay up. The link goes down and Po1 becomes the preferred IS-IS path:

pe1#conf t
pe1(config)#int et2
pe1(config-if-Et2)#no shut
Dec  6 11:54:45 pe1 Ebra: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet2 (et2 -> et2), changed state to up
Dec  6 11:54:45 pe1 Lag: %LAG-5-MEMBER_ADDED: Interface Ethernet2 (et2 -> et2) has joined Port-Channel2 (po2 -> po2)
Dec  6 11:54:47 pe1 Lldp: %LLDP-5-NEIGHBOR_NEW: LLDP neighbor with chassisId 001c.7369.a000 and portId "Ethernet2" added on interface Ethernet2
pe1(config-if-Et2)#int eth3
pe1(config-if-Et3)#shut
Dec  6 11:54:51 pe1 Ebra: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet3 (et3 -> et3), changed state to down
Dec  6 11:54:51 pe1 Lag: %LAG-5-MEMBER_REMOVED: Interface Ethernet3 (et3 -> et3) has left Port-Channel2 (po2 -> po2) due to: unknown reason
Dec  6 11:54:51 pe1 Lag: %LAG-5-MEMBER_REMOVED: Interface Ethernet2 (et2 -> et2) has left Port-Channel2 (po2 -> po2) due to: port-channel has no aggregable link up ports
Dec  6 11:54:51 pe1 Ebra: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-Channel2 (po2 -> po2), changed state to down
Dec  6 11:54:51 pe1 Isis: Instance 0: %ISIS-4-ISIS_ADJCHG: L2 Neighbor State Change for 0000.0000.0002 (pe2) on Po2 to DOWN: interface went down or no IP address on interface


pe1#show ip route 10.0.0.2/32 | beg 10.0.0.2
 I L2     10.0.0.2/32
           directly connected, Port-Channel1


pe1#show interfaces status 
Port       Name       Status       Vlan     Duplex Speed  Type            Flags Encapsulation
Et1        et1 -> et1 connected    in Po1   full   1G     EbraTestPhyPort                   
Et2        et2 -> et2 connected    in Po2   full   1G     EbraTestPhyPort                   
Et3        et3 -> et3 disabled     in Po2   full   10G    EbraTestPhyPort                   
Ma0                   connected    routed   a-full a-1G   10/100/1000                       
Po1        po1 -> po1 connected    routed   full   1G     N/A                               
Po2        po2 -> po2 notconnect   routed   full   unconf N/A                               


pe1#show isis interface brief 

IS-IS Instance: Gandalf VRF: default

Interface     Level IPv4 Metric IPv6 Metric Type           Adjacency
------------- ----- ----------- ----------- -------------- ---------
Loopback0     L2             10          10 loopback       (passive)
Port-Channel1 L2         100000      100000 point-to-point         1

 

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