IPv6: Static Routing
IPv6 Static Routing Overview
Static routes provide tools for restricting and troubleshooting routed traffic flows and in small networks can provide the simplest and most reliable configuration for IPv6 routing.
Static routes are manually configured in the routing table. A static route entry comprises the following:
IPv6 network prefix for the route's destination network
next-hop gateway, which can be one of the following:
either the link-local address and VLAN ID or the VLAN link to the next-hop router
a Global unicast address on the next-hop router
a "null" interface (the routing switch drops traffic forwarded to the null interface)
Optionally, a non-default administrative distance
[NOTE: ]
NOTE: To enable routing in both directions on a static route, you must configure reciprocal static routes on the routers at both ends of the route.
On a given routing switch you can create one static route or null route to a given destination. Multiple static or null routes to the same destination are not supported.
The routing switches can concurrently support a maximum of 256 IPv6 static routes and 256 IPv4 static routes.
For example, in Example of a routing domain, static routes enabling routed traffic between routers "A," "B," and "C" could be configured as follows:
Example of static route configuration in a network Router "A" Router "B" Router "C"
ipv6 route
2620:a::/64 2620:e::55:1
ipv6 route
2620:a::/64 2620:b::22:1
ipv6 route
2620:c::/64 2620:b::22:2
ipv6 route
2620:b::/64 2620:e::55:1
ipv6 route
2620:c::/64 2620:e::55:2
ipv6 route
2620:e::/64 2620:b::22:2 Note: next-hop addresses can be either global unicast or link-local.
Example of a routing domain Example of a routing domain Advantages of static routing
Static routing is relatively reliable and gives you tight control over traffic flow. You determine exactly which connections to use to forward traffic to each destination. In a given VLAN, you can use multiple IPv6 addresses to add multiple static routes in the VLAN. Other advantages include:
efficiency in a small network with few paths to manage
ease of configuration and maintenance
lower CPU utilization
Disadvantages of static routing
In a large or expanding network, configuring static routes for all the necessary routes can become increasingly complicated and time-consuming. Ensuring that all routes remain accurate can also add to the administrative burden. Each time you add a connection or change a route, you must configure the change on every routing device in the network. Also, routers do not automatically respond to a failed static connection, so traffic can be lost or misrouted.
[NOTE: ]
NOTE: Network management and monitoring applications such as PCM and PCM+ can detect failed static routes.
Static route types
You can configure these types of static IPv6 routes:
Standard: The static route consists of:
Destination network prefix
Link-local IPv6 address and VLAN ID of the (next-hop router) gateway IPv6 address
Interface-based: The static route consists of:
Destination network address or host and a corresponding network prefix
VLAN interface through which you want the routing switch to send traffic for the route
Null (discard): Null routes include the following:
Default: When IPv6 routing is enabled, a route for the ::1/128 network is created and traffic to this network is rejected (dropped). The loopback address (lo0) is entered as the gateway. This route is for all traffic to the "loopback" network, with the single exception of traffic to the host address of the switch's loopback interface.
Configured: Provides a route that is used as a backup route for discarding traffic where the primary route is unavailable. A configured null route consists of:
Destination network address or host and a corresponding network mask
Either the reject keyword (traffic dropped with ICMP notification to the sender) or blackhole keyword (traffic dropped without any ICMP notification).
Non-default null routes created with the reject or blackhole keywords use a gateway of zero (0).
Example of static routes in an ECMP application illustrates the default and configured null route entries in the switch's routing table. Static routing default settings
The routing switch applies default administrative distance and metric values to ensure that static routes are preferred over dynamic routes to the same destination.
Administrative distance: In the case of static routes, this is the value the routing switch uses to compare a static route to routes from other route sources to the same destination before placing a route in the routing table. The default administrative distance for static routes is 1, but can be configured to any value in the range of 1–255.
Metric: In the case of static routes, this is the value the routing switch uses when comparing a static route to routes in the routing table from any dynamic routes to the same destination. The metric for static routes is fixed, that is, always set to "1".
Static route states follow VLAN states
Static routes remain in the routing table only while the interface link to the next-hop router is up. If the next-hop router interface link goes down, the software removes the static route from the routing table. If the next-hop interface comes up again, the software adds the route back to the routing table.
This feature allows the routing switch to adjust to changes in network topology. The routing switch does not continue trying to use routes on unreachable paths, but instead uses routes only when their paths are reachable. Static routes for ECMP applications
Equal-cost multi-path routing (ECMP) is a routing strategy where next-hop packet forwarding to a single destination can occur over multiple "best paths." Each path has the same cost as the other paths, but a different next-hop router. In static routing, load-balancing can be achieved through ECMP. Example of static routes in an ECMP application illustrates static routes applied to an ECMP topology.
Example of static routes in an ECMP application Example of static routes in an ECMP application
The [no] ip load-sharing <2–4> command enables or disables load-sharing for both IPv4 and IPv6 applications and specifies the number of ECMP routes to allow. In the default configuration, load-sharing is enabled with four ECMP routes allowed. For more information, see Equal-cost multi-path routing (ECMP) for the Switch 2620-series.
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