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I am following the guide that is listed here for enabling LLDP on my Cisco Catalyst 3560G switch.

In short I entered the following into my switch.

Switch# configure terminal
Switch(config)# lldp run
Switch(config)# interface GigabitEthernet 0/5
Switch(config-if)# lldp transmit
Switch(config-if)# lldp receive
Switch(config-if)# end

What I am confused about however is that LLDP is enabled on all ports not just 0/5. This is actually what I wanted but I am curious if specifying 0/5 which I am forced to do or it doesn't recognize the command has any implications?

P.S.

If anyone has a better title for this let me know. I am very new to switches and layer 2 networking protocols.

  • What software version are you using? – Ron Maupin Jan 9 '17 at 5:03
  • Version 15.0(2)SE6 – mschuett Jan 9 '17 at 5:28
  • I believe that version may have LLDP globally disabled, but enabled on all the interfaces by default. When you globally enabled it, then it started working on all the interfaces. – Ron Maupin Jan 9 '17 at 5:33
  • was interface GigabitEthernet 0/5 doing pretty much nothing in that case? – mschuett Jan 9 '17 at 5:34
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    You can disable it globally, and it should still be enabled on the interfaces, but it won't actually work. It's like CDP where it is enabled on every interface by default, but you can enable or disable it on each interface, or shut it all down by disabling it globally. – Ron Maupin Jan 9 '17 at 5:41
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Summarizing the conversation of this post the command

interface GigabitEthernet 0/5

Was not doing anything since LLDP was enabled globally already. This would however allow you to disable LLDP on an interface and have it enabled on every other port. I don't see a huge use for enabling it on just one port other than being explicit but maybe someone else can fill in this knowledge gap.

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    With LLDP enabled, your network gear will happily tell anyone wanting to know about its make and model and possibly software version. This might not be necessary on access ports (but you also wouldn't discover an unexpected switch on such a port). Also, your gear will listen for incoming LLDP on all thos ports, which could be an attack vector. Thus, globally enabling LLDP increases the attack surface, – Gerben Jan 9 '17 at 10:05
  • I'm not a huge subscriber to the "security" aspect of disabling LLDP - the benefits of enabling it far outweigh the potential threat reduction gained by disabling it. The make of a switch can be deduced just as easily from the source MAC OUI in STP BPDUs (and you sure wouldn't turn that off) or IGMP group reports. People tend to forget that Availability is one of the core tenants of any security model, and I find LLDP to be essential for maintaining that. – Benjamin Dale Mar 11 '17 at 0:30
  • Having said all that, I have run into a few instances where IP handsets that doe not implement LLDP-MED correctly in some releases (Shortel, I'm looking at you), and disabling LLDP for those ports was the only workaround. – Benjamin Dale Mar 11 '17 at 0:30
  • You should accept your answer so that the question doesn't keep popping up forever, looking for an answer. – Ron Maupin May 10 '17 at 1:56
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The "LLDP run" command enables LLDP globally, but you still need to configure each interface with the transmit/receive commands for it to exchange frames with neighbors on that interface.

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