Does the Spark assigned gateway address change over time on a UFB connection?

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gplwhite

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Topic # 193416 10-Mar-2016 11:54

I have a UFB connection with a static IP address. I use a Fortigate firewall connected directly to the ONT - the firewall establishes the PPPoE connection so no need for a separate modem.

The Fortigate also supports failover to a secondary WAN connection if the primary WAN connection fails. I have configured the Fortigate to ping the assigned gateway address (222.152.45.105) to determine if the primary connection is up.

The problem I have is that several times recently the assigned gateway address has changed (ie: today it changed to 125.236.192.9), the ping to the old address fails and hence the health check causes the firewall to switch to the secondary connection. I have to reconfigure the health check with the new gateway address before the ping succeeds and the health check returns to normal.

Question: Is it common for the gateway address associated with a UFB static IP to change? Its happened 3 or 4 times in the last few months.

Would it be better to not ping the gateway, but instead ping something more static - such as 8.8.8.8? I assumed pinging the gateway would be less likely to cause a false positive if other non-connection specific internet faults occur.

Thoughts?

Thanks,
Greg

Lias

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Reply # 1510509 10-Mar-2016 12:34

I wouldn't have expected the gateway to ever change with a static IP.

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cbrpilot

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Reply # 1510517 10-Mar-2016 12:41

Yes, it can change, and we do not guarantee that it will be stable.

We did some tidy up activity at around 3am this morning that was no doubt the reason that it changed for you. The changes this morning may mean that it is now more stable (although that was not the main intend of the changes, it may be a side effect).

I'd be interested in hearing if it changes again, and what it changes to.

Dave.

My views are my own, and may not necessarily represent those of my employer.

gplwhite

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Reply # 1510551 10-Mar-2016 13:34

Thanks cbrpilot for confirming this. (Pity the helpdesk analyst I spoke to didn't have any knowledge of changes made - in fact they claimed there were no changes made last night).

What do people normally do for monitoring the health of their WAN link?

cbrpilot

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Reply # 1510735 10-Mar-2016 17:08

I cannot comment on what others do, but your router dynamically learns that gateway address when the PPP link comes up. If I were you I would seek to find out if there is a way of your connectivity monitoring to dynamically learn it.

Alternatively if you're only interested in whether the PPP link is up, you could just try pinging your own static IP. (i.e. the local end of the link). This should work so long you haven't hard coded the IP into your PPP config (which we don't recommend).

Dave.

My views are my own, and may not necessarily represent those of my employer.

sbiddle

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Reply # 1510782 10-Mar-2016 17:56

One person supports this post

Lias:

I wouldn't have expected the gateway to ever change with a static IP.

It might be static but it's still delivered over PPP - so a gateway can still easily change.

Lias

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Reply # 1510983 10-Mar-2016 23:10

Care to elucidate for my benefit?

I'm not totally network clueless, I have a current CCNA, albeit I do know many consider them fairly worthless pieces of paper.PPP was part of the curriculum, but PPP assigned IP addresses (along with most things internetish in reality) isn't.

I imagined it worked very much like DHCP, and that a static IP on an internet connection worked much like a DHCP reservation, and you'd always get a (generally) static gateway for whatever subnet your assigned address is in. A 2 minute google and looking at the config of my own connection put paid to that, but I can't say I fully understand it. My 2 minute interpretation is that PPP assigned IP's use a host only subnet because they don't need to know where to send stuff, it just dumps everything down the PPP connection, and let's whatevers at the far end deal with it, but I'm still not clear on why this results in changing gateways?

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yitz

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Reply # 1510996 11-Mar-2016 00:09

There may be multiple PPPoE access concentrators available (a role of the BNG) and it could depend on which one responds due to load balancing configuration. Although in this case it resulted from a logical network change.

Think of PPP encapsulation as a VPN rather than a LAN.