Junos
Junos

VRRP with single IP?

‎11-04-2008 06:37 AM

Unsure if this is a part of the VRRP spec, or Juniper's implimentation. All config examples I can see for VRRP show at least two IP's being used. Always a 'real' ip and a virtual-address. I'm looking to impliment VRRP on some J-series for many /28s and /29s. in some casess, /30. From what I can tell, it's not even possible on a /30 as you'd be using both available IPs for the routers. Here's a sample config which would show that no non-router IP'sare possible



unit 200 {
vlan-id 200;
family inet {
address 10.170.3.185/30 {
vrrp-group 0 {
virtual-address 10.170.3.186;
}
}
}
}

 

Is this the only way VRRP can be implemented? Any other way that I can create gateway redundancy to hosts without requiring their routing tables to be updated? This is on a J2350.

 

 

6 REPLIES 6
Junos

Re: VRRP with single IP?

‎11-04-2008 07:16 AM
No. What you want to do is not possible. You will always need a minimum of 3 IP address to setup VRRP. 1 for the local router, 1 for the remote router and 1 virtual IP address. The is the fundemental way in which VRRP works. You will therefor always have to have a /29 a the minimum subnet size. A /29 will also allow 3 additional hosts on the subnet. A /30 will not work.
Junos

Re: VRRP with single IP?

‎11-04-2008 08:11 AM

Bummer. Any VRRP alternatives? I was used to Carp on OpenBSD/FreeBSD where one could have *just* the virtual IP. Or, any kludge where the virtual ip exists outside of the 'real' ip where I could RFC1918 IP's for the 'real' IPs just to have them there? I'd think not since the virtual-address seems to imply a /32.

Junos

Re: VRRP with single IP?

‎11-04-2008 11:46 AM

Actually, you *can* do VRRP with just two addresses.  This makes use of the real address from the master as the shared address.  As such, the master always must be master when it is live.  It is preemptive so it will force itself to be master when it comes back online.  If you do this, it may break interface tracking because you're trying to override the requirement that the master interface is always master while it is alive.

 

This isn't necessarily what you're after but it is a way of doing VRRP without three addresses. 

 

Rgds,

 

Guy 

Junos

Re: VRRP with single IP?

‎11-05-2008 04:50 PM

I would not use a vrrp alternative since vrrp is a widely-deployed standard and an alternative proto would be non-standard.  What is the reason for needing a /30 and not being able to use a /29?

 

Junos

Re: VRRP with single IP?

‎05-27-2019 07:55 AM

would you be able to post the config snippet on master and slave rotuers using /30 (with only two IPs).

Junos

Re: VRRP with single IP?

‎06-04-2019 12:46 AM

Wow...  That's an old thread Smiley Happy

 

Looking again at it, I can't think of a situation in which a VRRP address on a /30 would be useful although it would technically work.  There can only be two hosts on a /30, so both would be VRRP members.  There would be no other hosts to actually use the VRRP address as the default gateway.

 

On a /29, you could have up to four clients along with the two VRRP members.  Those VRRP members can work with just two addresses.  On the "primary" host, you would use the same address as the physical interface as your VRRP address.  You'd also set the VRRP to revert when the primary host recovers.  On the secondary host, you would have a unique physical address and use the physical address of the primary host as your VRRP address.

 

I don't have a spelled out example to hand but I hope that helps.

 

Rgds,

 

Guy