A routing table is present on all nodes.
Note
The switch requires routing protocols, such as OSPFv3 to exchange IPv6 routing prefixes.
For each incoming packet, the switch checks the destination neighbor cache first. If the destination is not in the destination neighbor cache, the routing table determines:
the next-hop interface (the interface used for forwarding)
the next-hop address
Note
The system uses the IPv6 Neighbor Cache for on-link, directly-connected destinations only. Off-link destinations go through a next-hop router, as determined by the next-hop address lookup.
IPv6 routes in a routing table can be:
directly attached network routes using a 64-bit prefix
remote network routes using a 64-bit or lower prefix
host routes using a 128-bit prefix length
the default route using a prefix of ::/0
BGP+ (over 6in4 tunnels)
BGPv6
IPv6 Shortcuts (over Fabric Connect)
OSPFv3
RIPng
You can redistribute IPv6 routes between any of these routing protocols.
To configure IPv6 routing on a VLAN, an IP address is assigned to the VLAN. This IP address is not associated with any particular physical port, but is used on all ports where this VLAN is a member.
On a brouter port, a single port VLAN is used to route the traffic. IPv4 and IPv6 traffic is routed in the single-port brouter VLAN.
Other VLANs (which are multiple port VLANs) can bridge and route the traffic.
The switch supports IPv6 routing between subnets.
When you add an IP address to the VLAN, the system maps an IP subnet to the VLAN.
As shown in the following figure, although VLAN 1 and VLAN 2 reside on the same switch, for traffic to flow from VLAN 1 to VLAN 2, you must route the traffic.
You must enable IPv6 forwarding to route IPv6 traffic between VLANs. And you must enable IPv6 both globally and on a specific VLAN basis in order for forwarding to function. You can enable or disable IPv6, either globally or on a specific VLAN basis.
IPv6 forwarding is enabled by default.
When you configure routing on a VLAN, an IPv6 address assigned to the VLAN is the VLAN IP interface.
The VLAN IPv6 address can be reached through any VLAN port, and frames route from the VLAN through the gateway IPv6 address.
You can forward traffic to any IPv6 subnet in the switch. A VLAN can be reached only if it has an IPv6 interface configured on it.
Because a port can belong to multiple VLANs, a one-to-one correspondence no longer exists between the physical port and the router interface when VLAN tagging is enabled.
If you do not enable VLAN tagging a single port can belong only to one port-based VLAN, but that same single port can belong to multiple policy-based VLANs.
As with any IPv6 address, you can use any VLAN IP interface for device management.
For the Simple Network Management Protocol (SNMP) or Telnet management, you can use any VLAN IP interface to access the switch while routing is enabled on the VLAN.
A brouter port is a single-port VLAN that can route IP packets and bridge all nonroutable traffic.
The difference between a brouter port and a standard protocol-based VLAN configured for routing is that the routing interface of the brouter port is not subject to the spanning tree state of the port. A brouter port can be in the blocking state for nonroutable traffic while it routes IP traffic.
Note
Because a brouter port is a one-port VLAN, each brouter port decreases the number of available VLANs by one and uses one VLAN ID.
Static routes provide an alternative method for establishing route reachability.
Static routes, with dynamic routes, provide routing information from the forwarding database.
Only enabled static routes whose nexthop address is reachable are submitted to the Route Table Manager (RTM), which determines the best route based on reachability, route preference, and cost.
The RTM communicates all updates to best routes.
If the nexthop is not reachable you can use the show ipv6 route static command to display the status. If the nexthop is not reachable, the status is TryToResolve and the system does not display the route in the RTM until the nexthop address is resolved.
For directly-connected IPv6 Subnets you do not need to specify a nexthop address; you can specify outgoing Tunnel-ID, VLAN, or port. If you use outgoing Tunnel-ID, VLAN, or port, the implied nexthop value is 0::0.
When you configure IPv6 static routes only by interface (VLAN or brouter), it lets the traffic to reach IPv6 prefixes configured on the link that is directly connected to the interface provided in the static route configuration. For example: ipv6 route 180:0:0:0:0:0:0:0/64 cost 1 vlan 631.
When you configure static routes with a link-local nexthop, you must also specify the outgoing Tunnel-ID, VLAN, or port because link-local addresses are ambiguous unless the proper interface binding is attached. For example: ipv6 route 1234::/64 cost 1 next-hop fe80::1 vlan 1900.
You must provide the following options to configure a static route:
local or nonlocal hop option
Configure a static route either with a next hop that exists on a locally attached network or a next hop that is reachable through a dynamic route. The static route is available as long as the next hop is reachable.
route preference
You can specify the route preference for the static routes as follows:
Global value for all static routes: the preference is either static or dynamic routes.
Preference for each static route entry: if specified, this value overrides the global value for the entry which provides flexibility to change the general behavior of a specific static route.
Administrative status
Controls when the static route is considered for forwarding. Administrative status differs from the operational status. An admin-enabled static route can still be unreachable and not used for forwarding. An admin-disabled static route is operationally a nonexistent route.
Multiple static routes
Specify alternative paths to the same destination. Multiple static routes provide stability and load balancing.
To configure a default static route, supply a value of 0 for the prefix and the prefix length.
The following table describes events that affect static route operation.
|
Action |
Result |
|---|---|
|
Change the administrative status of the static route |
Makes the static route unavailable for forwarding You can use one CLI command to administratively enable or disable all static routes as follows ipv6 route static enable. You can administratively disable all routes but preserve the static route configuration when you use the CLI command: no ipv6 static route enable. |
|
Delete the IPv6 addresses of a VLAN or brouter port |
Permanently deletes the static routes with the corresponding local neighbors from the RTM, the forwarding database, and the configuration database |
|
Delete a VLAN |
Removes static routes with a local next-hop option from the configuration database. Static routes with a nonlocal next-hop option become inactive (they are removed from the forwarding database). |
|
Disable forwarding on a VLAN or brouter port |
Static routes reachable through the locally attached network become inactive |
|
Disable a VLAN or brouter port |
Makes the static route inactive |
|
Disable IPv6 forwarding globally |
Stops forwarding all IPv6 traffic |
|
Learn changes about a dynamically learned neighbor |
After a neighbor becomes unreachable or is deleted, the static route with the neighbor becomes inactive, and the configuration is not affected. The static route with the neighbor becomes active in the configuration and is added to the RTM and forwarding database when the neighbor becomes reachable. |
|
Enable a static route |
Adds the route to the RTM to change certain static routes to active. |
|
Delete a static route |
Permanently deletes a static route from the configuration. |
|
Disable a static route |
Stops traffic on the static route but does not remove the route from the configuration. |
|
Change a route preference |
After the static route preference changes, the best routes for the entries use both static and dynamic paths. |
|
Delete or disable a tunnel |
Removes the tunnel entry from the forwarding table |
|
Enable a tunnel |
Activates the tunnel static routes and adds an entry to the forwarding table. |
The local-nexthop flag is not required for IPv6.
An IPv4 device cannot learn a neighbor ARP entry unless the device uses a local route entry.
In IPv6, a host can learn a neighbor entry if the device is physically connected to the neighbor (one hop).
The static route becomes active when the next hop is reachable by a dynamic route neighbor resolution. The static route takes the forwarding information from the dynamic route. If the next hop is reachable using a local route, the neighbor resolution is required.
The static route table is separate from the system routing table that the router uses to make forwarding decisions.
You can use the static route table to directly change static routes.
Although the tables are separate, the system routing table automatically reflects the static routing table manager entries if the next-hop address in the static route is reachable and if the static route is enabled.
The static route table is indexed by four attributes:
destination network
destination mask
next hop
interface
You can insert static routes by using the static route table, and you can delete static routes by using either the static route table or the system routing table. For information on route scaling, see Fabric Engine Release Notes.
Important
The system routing table stores only active static routes with the best route preference. A static route is active only if the route is enabled and if the next-hop address is reachable; for example, if a valid IPv6 neighbor cache entry exists for the next hop.
You can enter multiple routes (for example, multiple default routes) that use different costs and the lowest cost route that is reachable, the system displays the lowest cost route in the routing table.
If you enter multiple next hops for the same route with the same cost, the switch does not replace the existing route.
If you enter the same route with the same cost and a different next hop, the switch uses the first route. If that first route becomes unreachable, the system activates the second route, with a different next-hop, with no connectivity loss.