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Extreme Certified Professional - Extreme Switching study materials
Extreme Certified Professional - Extreme Switching study resources

Extreme Certified Professional - Extreme Switching: IP Routing and Layer 3 Forwarding on Switches

Extreme Certified Professional - Extreme Switching · Work through your exam, one topic at a time.

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IP Routing and Layer 3 Forwarding on Switches

Domain 5 - IP Routing and Layer 3 Forwarding on Switches. Questions test how ExtremeXOS turns a VLAN into a routed interface, how connected and static routes appear in the routing table, and how OSPF and VRRP are enabled with accurate syntax.

Making a switch route

  • Routing requires an IP address on a VLAN: configure vlan Users ipaddress 10.10.10.1/24.
  • Global IP forwarding is normally on, but the VLAN interface must also forward: enable ipforwarding vlan Users.
  • One primary IP per VLAN. Directly connected networks are installed automatically and appear in show iproute; hosts are resolved through ARP, shown by show iparp.

Static and dynamic routing

  • Default route: configure iproute add default 0.0.0.0/0 10.10.10.254. Specific route: configure iproute add 10.20.0.0/16 10.10.10.254.
  • OSPF: enable ospf, configure ospf routerid 10.0.0.1, configure ospf vlan Users area 0.0.0.0, then check show ospf and show ospf interfaces.
  • VRRP: create vrrp vlan Users vrid 10, configure vrrp vlan Users vrid 10 add 10.10.10.254, configure vrrp vlan Users vrid 10 priority 200 on the preferred master, enable vrrp vlan Users vrid 10 on both. The virtual IP must differ from either router's real VLAN IP.
  • IPv6 follows the same model: assign an IPv6 address and enable IPv6 forwarding.

Worked example

VLAN 10 is 10.10.10.0/24 and VLAN 20 is 10.20.20.0/24, both with the switch at .1. A host on VLAN 10 with gateway 10.10.10.1 pings a host on VLAN 20. Both networks are directly connected, so no static route is needed: the switch looks up 10.20.20.x, finds the connected route out of VLAN 20, ARPs for the host and forwards. Now add remote network 10.30.30.0/24 behind 10.10.10.254: either a static route configure iproute add 10.30.30.0/24 10.10.10.254 or OSPF on VLAN 10 in area 0.0.0.0. Reasoning: the switch only needs the next hop toward networks it is not attached to, and the far router needs a return path.

Traps

  • Hosts with the wrong default gateway, or a gateway pointing at a VRRP address that no router owns because VRRP was never enabled.
  • Overlapping subnets on two VLANs, which breaks interface activation.
  • Skipping enable ipforwarding vlan, so the interface answers pings but does not route.
  • Configuring the router's real IP as the VRRP virtual IP.
  • OSPF area mismatch, or forgetting enable ospf, so neighbours never reach FULL.