Hi All
I
have gone through various documents on UDLD, Loopguard etc, with Rapid
STP, normal STP .... Just wanted some kind of confirmation/validation
here:
1)
UDLD aggressive - will be enabled globally for IOS devices.. for Cat OS
it is enabled per interface, as it cannot be enabled globally.. ( cat
OS has UDLD normal mode in global mode).. i have also gone thro various
scenarios - like enabling UDLD aggressive on one side,and the other
side having normal mode or no UDLD enabled !UDLD can be enabled with no
issues on one-side.. UDLD normal puts the port on inconsistent state,
and UDLD aggressive err-disables the port.. Is that right ?
2)
UDLD aggressive with Rapid STP - UDLD takes 45 secs to detect
unidirectional link (15 sec message time), and 8 more secs.. With Rapid
STP the convergence time is less and UDLD might not be useful in this
case .. even with lowest message time 7 secs, it takes 21 secs to
converge ... we can then use loopguard to detect unidirectional link
with RSTP .. Is that right ? I saw a lot of posts from Francois about
UDLD and Rapid STP timers which is of interest...
3)
loopguard - as said above, loopguard will be used to detect
unidirectinal links with RSTP.. when enabled globally, it enables
loopguard on all ports (root, desig, blocked) etc.. is this fine ?
also, how much time (in secs) will loopguard take to put the port on
"loop inconsistent" mode.. are there any timers involved with loopgurad
?
4)
Rapid STP with PVST on other side - when migrating PVST to Rapid PVST,
we can have situations where we have Rapid STP in one side, and PVST on
other.. In this case the network will work with normal STP timers (50
sec) convergence.. and UDLD would work good in this case.. Is that
right ?
5)
best practice - enabled loopguard & udld globally on all ports,
whether the STP is rapid or PVST, or the switch is root or designated..
is that right ?
Hoping to hear..
Raj
I agree with your most of the point which you have mentioned in your thread just my thoughts and recommendation on the thread.
UDLD is disabled globally and enabled in readiness on fiber ports by default. Because UDLD is an infrastructure protocol that is necessary between switches only, UDLD is disabled by default on copper ports. Copper ports tend to be used for host access.
Note: UDLD must be enabled globally and at the interface level before neighbors can achieve bidirectional status. In CatOS 5.4(3) and later, the default message interval is 15 seconds and is configurable between 7 and 90 seconds.
and yes port goes to err- disable state once any loop is dedected where UDLD is enabled and normal recommendation for Normal mode UDLD is sufficient in the vast majority of cases if you use it properly and in conjunction with the appropriate features and protocols. These features/protocols include:
Cisco recommends the enablement of UDLD normal mode on all point-to-point FE/GE links between Cisco switches in which the UDLD message interval is set to the 15-second default. This configuration assumes the default 802.1d spanning tree timers. Additionally, use UDLD in conjunction with loop guard in networks that rely on STP for redundancy and convergence. This recommendation applies to networks in which there are one or more ports in the STP blocking state in the topology and regarding Loop guard is only useful in switched networks where switches are connected by point-to-point links.Loop guard isolates the failure and lets spanning tree converge to a stable topology without the failed link or bridge. Loop guard prevents STP loops with the speed of the STP version in use. There is no dependency on STP itself (802.1d or 802.1w) or when the STP timers are tuned. For these reasons, implement loop guard in conjunction with UDLD in topologies that rely on STP and where the software supports the features.
