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I have a couple of questions regarding Logical Systems ( Routers )
1. If I have a router working at the moment and then I alter the configuration to make the base node into a logical system, to perpare for more logical systems, what impact is there on the running node? do routing processes retstart etc when I perform the commit?
2. Can a logical system be ssh/telneted into directly via its unique loopback IP?
3. if you have a fully redundant node in terms of hardware and have configured logical systems, can you perform an ISSU?
anyone think of anything particular to bear in mind when using this type of setup?
Adding Logical Systems should not have an impact on the existing systems. New, separate daemons will be created without impact on the original ones and routing processes should not restart.
Yes, you can telnet into an LS on its own routing table. That should not necessarily be a lo0 interface address.
ISSU is only supported on the master LS. See http://www.juniper.net/techpubs/en_US/junos9.6/information-products/topic-collections/swconfig-high-availability/issu-system-requirements.html#section-issu-system-requirements
I have never tested this, but here are my thoughts anyway.
There are 2 components to ISSU.
First, there is the hardware component. All of the FPCs, PICs or DPCs on your router should support ISSU. If not, they will be reset when you switchover from one RE to the other RE (which has a different code). Assuming your Logical Systems to be implemented on ISSU supported hardware, you should be fine. If not, you would suffer from the same effect outside of LS as well.
Second, there is the software component. Obviously the kernel and so on must support it, but more visible is the protocol support. You need to make sure you can switchover from one RE towards the other without losing adjacencies, peerings, .... , so basically neighboring routers can't tell you've switched. This is a hard thing to do (especially the corner cases, ie when you switchover in an unstable network). In JUNOS, we do this through Non Stop Routing (NSR). Today, we're supporting close to all protocols (you'll find them in the manuals).
What is not supported is the fact that these protocols could be running from a separate LS. A protocol that is not supported will break up its neighborships as it will loose synchronization during the switchover (ie TCP windows not be corresponding).
So the effect of the latter in the LS will depend on the protocols that you use. If you have an LS with static routes, I would imagine the impact is minimal. If you take protocols like an IGP, BGP, PIM, .... you will also be depending on your neighbors on how fast they can build the new neighborship.
But a reboot is definitely not what I'm expecting. Your LS routing table will be impacted though and hence also your forwarding for some time.
how can i configure logical router?
have a look at http://www.juniper.net/techpubs/en_US/junos9.6/information-products/topic-collections/config-guide-routing/id-10523666.html#id-10523666.