implementing load balancing through IS-IS:
Networking Requirements
As shown in Figure 1:
- CX- A, CX- B, CX- C, and CX- D run IS-IS to implement interconnection in the IP network.
- CX- A, CX- B, CX- C, and CX- D are Level-2 routers in area 10.
- Load balancing is required to transmit the traffic of CX- A to CX- D through CX- B and CX- C.
Figure 1 Networking diagram of configuring IS-IS load balancing
Device
|
Interface
|
IP Address
|
Device
|
Interface
|
IP Address
|
CX-A
|
GE 3/0/0
|
172.16.1.1/24
|
CX-C
|
POS 1/0/0
|
10.1.2.2/24
|
POS 1/0/0
|
10.1.1.1/24
|
POS 2/0/0
|
192.168.1.1/24
| ||
POS 2/0/0
|
10.1.2.1/24
| ||||
CX-B
|
POS 1/0/0
|
10.1.1.2/24
|
CX-D
|
GE 3/0/0
|
172.17.1.1/24
|
POS 2/0/0
|
192.168.0.1/24
|
POS 1/0/0
|
192.168.0.2/24
| ||
POS 2/0/0
|
192.168.1.2/24
|
Configuration Roadmap
The configuration roadmap is as follows:
- Enable basic IS-IS functions on each CX device to implement interconnection.
- Cancel load balancing and check the routing table.
- Configure load balancing on CX- A and check the routing table of it.
- (Optional) Configure the preference for equal-cost routes on CX- A.
Data Preparation
To complete the configuration, you need the following data:
- Levels and the area addresses of the four CX devices.
- Number of load balancing paths on CX- A is 1.
- Preference value of equal-cost routes on CX- C is 1.
Procedure
- Assign an IP address for each CX device.The configuration details are not mentioned here.
- Configure basic IS-IS functions.
- Cancel load balancing on CX- A.
[CX-A] isis 1[CX-A-isis-1] maximum load-balancing 1[CX-A-isis-1] quit# Check the routing table of CX- A.[CX-A] display isis routeRoute information for ISIS(1)
-----------------------------
ISIS(1) Level-2 Forwarding Table
--------------------------------
IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags
-------------------------------------------------------------------------
192.168.1.0/24 20 NULL P2/0/0 10.1.2.2 A/-/L/-
10.1.1.0/24 10 NULL P1/0/0 Direct D/-/L/-
172.16.1.0/24 10 NULL GE3/0/0 Direct D/-/L/-
172.17.1.0/24 30 NULL P1/0/0 10.1.1.2 A/-/L/-
10.1.2.0/24 10 NULL P2/0/0 Direct D/-/L/-
192.168.0.0/24 20 NULL P1/0/0 10.1.1.2 A/-/L/-
Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
U-Up/Down Bit Set
As shown in the routing table, when the maximum number of equal-cost routes for load balancing is set to 1, the next hop to network segment 172.17.1.0 is 10.1.1.2. This is because the system ID of CX- B is small. IS-IS chooses the route with the next hop being 10.1.1.2 as the unique optimal route. - Restore the default number of load balancing paths on CX- A.
[CX-A] isis 1[CX-A-isis-1] undo maximum load-balancing[CX-A-isis-1] quit# Check the routing table of CX-A.[CX-A] display isis routeRoute information for ISIS(1)
-----------------------------
ISIS(1) Level-2 Forwarding Table
--------------------------------
IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags
-------------------------------------------------------------------------
192.168.1.0/24 20 NULL P2/0/0 10.1.2.2 A/-/L/-
10.1.1.0/24 10 NULL P1/0/0 Direct D/-/L/-
172.16.1.0/24 10 NULL GE3/0/0 Direct D/-/L/-
172.17.1.0/24 30 NULL P1/0/0 10.1.1.2 A/-/L/-
P2/0/0 10.1.2.2
10.1.2.0/24 10 NULL P2/0/0 Direct D/-/L/-
192.168.0.0/24 20 NULL P1/0/0 10.1.1.2 A/-/L/-
Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
U-Up/Down Bit Set
As shown in the routing table, the default value is used when load balancing is canceled. The two next hops of CX-A, that is, 10.1.1.2 (that is, CX- B) and 10.1.1.2 (that is, CX- C), are valid routes. This is because the default value of the maximum equal-cost routes is 3. - (Optional) Configure the preference of equal-cost routes on CX-A.If you do not perform load balancing through CX- B and CX- C, configure the preference of the equal-cost routes and specify the next hop.
[CX-A] isis[CX-A-isis-1] nexthop 10.1.2.2 weight 1[CX-A-isis-1] quit - Verify the configuration.# Check the routing table of CX- A.
[CX-A] display isis routeRoute information for ISIS(1)
-----------------------------
ISIS(1) Level-2 Forwarding Table
--------------------------------
IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags
--------------------------------------------------------------------------------
192.168.1.0/24 20 NULL P2/0/0 10.1.2.2 A/-/L/-
10.1.1.0/24 10 NULL P1/0/0 Direct D/-/L/-
172.16.1.0/24 10 NULL GE3/0/0 Direct D/-/L/-
172.17.1.0/24 30 NULL P1/0/0 10.1.2.2 A/-/L/-
10.1.2.0/24 10 NULL P2/0/0 Direct D/-/L/-
192.168.0.0/24 20 NULL P1/0/0 10.1.1.2 A/-/L/-
Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
U-Up/Down Bit Set
As shown in the routing table, because the preference (metric is 1) of next hop 10.1.2.2 (that is, CX- C) is higher than that of next hop 10.1.1.2 (that is, CX- B), IS-IS chooses the route with the next hop being 10.1.2.2 as the optimal route.
Configuration Files
- Configuration file of CX- A
#
sysname CX-A#
isis 1
is-level level-2
network-entity 10.0000.0000.0001.00
nexthop 10.1.2.2 weight 1
#
interface GigabitEthernet3/0/0
ip address 172.16.1.1 255.255.255.0
isis enable 1
#
interface Pos1/0/0
link-protocol ppp
ip address 10.1.1.1 255.255.255.0
isis enable 1
#
interface Pos2/0/0
link-protocol ppp
ip address 10.1.2.1 255.255.255.0
isis enable 1
#
return
- Configuration file of CX- B
#
sysname CX-B#
isis 1
is-level level-2
network-entity 10.0000.0000.0002.00
#
interface Pos1/0/0
link-protocol ppp
ip address 10.1.1.2 255.255.255.0
isis enable 1
#
interface Pos2/0/0
link-protocol ppp
ip address 192.168.0.1 255.255.255.0
isis enable 1
#
return
- Configuration file of CX- C
#
sysname CX-C#
isis 1
is-level level-2
network-entity 10.0000.0000.0003.00
#
interface Pos1/0/0
link-protocol ppp
ip address 10.1.2.2 255.255.255.0
isis enable 1
#
interface Pos2/0/0
link-protocol ppp
ip address 192.168.1.1 255.255.255.0
isis enable 1
#
return
- Configuration file of CX- D
#
sysname CX-D#
isis 1
is-level level-2
network-entity 10.0000.0000.0004.00
#
interface GigabitEthernet3/0/0
ip address 172.17.1.1 255.255.255.0
isis enable 1
#
interface Pos1/0/0
link-protocol ppp
ip address 192.168.0.2 255.255.255.0
isis enable 1
#
interface Pos2/0/0
link-protocol ppp
ip address 192.168.1.2 255.255.255.0
isis enable 1
#
return
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