To enable communication between the NetScaler ADC and servers in subnets connected through a router, you must configure at least one subnet IP address that belongs to the subnet of the directly connected interface to the router. The ADC uses this subnet IP address to communicate with servers in subnets that can be reached through the router.
Consider an example of a load balancing setup in which load balancing virtual server LBVS1 on NetScaler ADC NS1 is used to load balance servers S1, S2, S3, and S4, which are connected to NS1 through router R1.
S1 and S2 belong to same subnet, 192.0.2.0/24, and are connected to R1 through L2 switch SW1. S3 and S4 belong to a different subnet, 18.104.22.168/24, and are connected to R1 through L2 switch SW2.
NetScaler ADC NS1 is connected to router R1 through subnet 22.214.171.124/24. SNIP address SNIP1, which belongs to the same subnet as the directly connected interface to the router (126.96.36.199/24), is configured on NS1. NS1 uses this address to communicate with servers S1 and S2, and with servers S3 and S4.
For more information about configuring load balancing on a NetScaler ADC, see Load Balancing.
As soon as address SNIP1 is configured, NS1 broadcasts ARP announcement packets for SNIP1.
NS1’s routing table consists of route entries for S1, S2, S3, and S4 through R1. These route entries are either static route entries or advertised by R1 to NS1, using dynamic routing protocols.
Services SVC-S1, SVC-S2, SVC-S3, and SVC-S4 on NS1 represent servers S1, S2, S3, and S4. NS1 finds, in its routing tables, that these servers are reachable through R1. NS1 sends them monitoring probes at regular intervals, from address SNIP1, to check their health.
For more information about IP routing on a NetScaler ADC, see IP Routing.
Following is the traffic flow in this example:
- Client C1 sends a request packet to LBVS-1. The request packet has:
- Source IP = IP address of the client (198.51.100.10)
- Destination IP = IP address of LBVS-1 (203.0.113.15)
- LBVS1 of NS1 receives the request packet.
- LBVS1's load balancing algorithm selects server S3.
- NS1 checks its routing table and finds that S3 is reachable through R1. SNIP1 (188.8.131.52) is the only IP address on NS1 that belongs to the same subnet as router R1, NS1 opens a connection between SNIP1 and S3 through R1.
- NS1 sends the request packet to R1 from SNIP1. The request packet has:
- Source IP address = SNIP1 (184.108.40.206)
- Destination IP address = IP address of S3 (220.127.116.11)
- The request reaches R1, which checks its routing table and forwards the request packet to S3.
- S3’s response returns by the same path.