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I'm looking for a simple way to allow a router discover communication devices over a LAN. I've heard a bit about DLEP and LLDP, but aside from understanding that LLDP is older, and DLEP has only recently achieved an RFC status, I couldn't find much more.

What I'm interested to know is:

  1. What is the adoption status of any of the two? Is any of them widely used?
  2. Does one of them has a significant advantage over the other, a "killer feature" that makes it much more relevant and useful?

Thanks

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin ♦
    Feb 19, 2018 at 20:42

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Trying to compare the two protocols is really comparing apples and oranges. They are two separate protocols for two separate jobs.

As Zac67 points out, LLDP is widely supported by business network devices, but it is limited to the link. It uses a layer-2 multicast address which will not be forwarded beyond the interface.

DLEP is used between a router and modem to help the router make better routing decisions. It is not really a device discovery protocol the way LLDP is. I know that some Cisco devices support DLEP, but the RFC was only posted a few months ago, so it will be a while before it is widely supported.

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  • Do you know of protocols similar to DLEP? All I could find is R2CP that its RFC is stated to be no longer active.
    – DannyL
    Dec 31, 2017 at 14:26
  • What, specifically, are you trying to achieve? Explain it in detail. We don't want to get into an X-Y problem where you are trying to focus on a solution, rather than the problem.
    – Ron Maupin ♦
    Dec 31, 2017 at 14:31
  • I have a LAN with one or more radio modems. I don't know in advance of what type or how many there are. A router is connected to that LAN and I want it to be able to discover the connected radio modems without needing to check every possible IP address in the segment. Also the discovery should be reliable, meaning that if the router and radio modem are configured correctly, the router will discover the radio modem with very high probability.
    – DannyL
    Dec 31, 2017 at 15:30
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    @DannyL In the scenario in your last comment, it is very likely that LLDP (or DLEP or CDP or whatever) would have to already be activated and configured on the radio modems before you want to discover them. Unless they were configured that way and LLDP was never used, you won't be able to just turn on LLDP on your other devices and discover the radios. The only other situation that might help is the the radios come with a discovery protocol turned on by default and it hasn't been turned off.
    – Todd Wilcox
    Jan 3, 2018 at 19:44
  • I do take into account that whichever protocol I'll want to use, both the router and radio modem will have to be configured to use it once they're up and running. My question is assuming that and the above scenario.
    – DannyL
    Jan 3, 2018 at 20:12
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I haven't seen a device supporting DLEP yet. LLDP is widely supported but only works on the link level, so it would discover only directly connected devices. LLDP messages from devices behind (802.1D compliant) switches will not reach you. However, given access to the discovered devices you could use SNMP to query their LLDP database and work your way through the network.

What you're looking for may be ICMP Router Discovery Protocol for IPv4 and Neighbor Discovery Protocol for IPv6.

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  • Hi, thanks for the quick response. However these two protocols you suggest are mainly for router detection by hosts. I'm looking for modems and radios detection by a router.
    – DannyL
    Dec 31, 2017 at 11:28

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