Static route removed during interface delete/re-add if hostmodel is set to strong (Doc ID 2158937.1)

Last updated on APRIL 20, 2023

Applies to:

Symptoms

 Background information (requirements):

By default, a multihomed host routes its network traffic based on the longest matching route to the traffic's destination in the routing table. When multiple routes of equal length to the destination exist,   Oracle Solaris applies Equal-Cost Multi-Path (ECMP) algorithms to spread the traffic across those routes. This type of traffic routing configuration is called asymmetric routing. Solairs 11 introduce a property called "hostmodel" that controls the behavior of IP packets that are received or transmitted through a multihomed host. The hostmodel property can have one of three possible values:

weak (asymmetric routing)
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Corresponds to the weak ES model as defined in RFC 1122. With this value, a multihomed host uses asymmetric routing:

- Outgoing packets - The source address of the packet going out need not match the address configured on the outgoing interface.
- Incoming packets - The destination address of the incoming packet need not match the address configured on the incoming interface

This setting is similar to the ip_strict_dst_multihoming = 0 setting through ndd.

strong (symmetric routing)
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Corresponds to the strong end system (ES) model as defined in RFC 1122. This value implements symmetric routing:

- Outgoing packets - The source address of the packet going out must match the address configured on the outgoing interface.
- Incoming packets - The destination address of the incoming packet must match the address configured on the incoming interface.

This setting is similar to the "ip_strict_dst_multihoming = 1" through ndd, with an additional requirement that packets originated from the host are only sent out on interfaces where the IP source address of the outgoing packet is an address that is configured on the outgoing interface.

src-priority
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Configures packet routing by using preferred routes. If multiple destination routes exist in the routing table, then the preferred routes are those that use interfaces on which the IP source address of an outgoing packet is configured. If no such routes exist, then the outgoing packet will use the longest matching route to the packet's IP destination.

Symptom

When the hostmodel is set to "strong" or "src-priority" to protect against IP-spoofing, the static routes, added by the route(1M) command, are bound to the configured interfaces belonging to the subnets of the gateways. Therefore, if that interfaces are put down or unplumbed the static routes are deleted from the routing table. After the interfaces are up again, these static routes must be added again.

Changes

 The customer needs to set the hostmodel=strong

Cause

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