Hello padding

Load isis.cfg

#IOS-XE
config replace flash:isis.cfg

#IOS-XR
configure
load bootflash:isis.cfg
commit replace
y

Configure R1 and XR2 so that Hellos are only padded the first six times.

Answer

#R1
int Gi2.12
 no isis hello padding

! or

router isis
 no hello padding [multi-point|point-to-point]

#XR2
router isis 1
 int Gi0/0/0/0.1920
  hello-padding sometimes [level 2]

Explanation

By default, the router will always pad Hellos. This can be considered an unnecessary waste of bandwidth, as once you’ve verified MTU via the padded Hellos, you no longer really need to continue to pad Hellos.

When using the above configuration, the router will only pad the first 6 Hellos. After this, all subsequent Hellos are not padded, which saves some bandwidth.

If for some reason you wanted to never pad Hellos, not even at the beginning of the adjacency, you can use no isis hello padding always under the interface on IOS-XE, or hello-padding disable on IOS-XR. This is similar to OSPF’s ip ospf mtu-ignore setting.

Verfiy that R1 is not padding Hellos on Gi2.12:

When you use no isis hello padding always, you will instead see “Never pad hello PDU”:

I cannot find an equivalent way to verify on IOS-XR.