Hi Krasimir, Krzysztof, On 24 July 2018 at 17:25, Krasimir Avramski <kr...@smartcom.bg> wrote: > It is used in Access Nodes(default route to AGN) with > LDP-DOD(Downstream-on-Demand) Seamless MPLS architectures - RFC7032 > A sample with LDP->BGP-LU redistribution on AGN is here.
Thanks Krasimir. Sorry for the delay, I read https://tools.ietf.org/html/rfc7032, https://tools.ietf.org/html/rfc5283 and https://tools.ietf.org/html/draft-ietf-mpls-seamless-mpls-07 before responding. On 25 July 2018 at 09:14, Krzysztof Szarkowicz <kszarkow...@gmail.com> wrote: > The purpose of “Longest Match for LDP” is to be able to distribute /32 LDP > FECs, if corresponding /32 routes are not available in IGP. > So, on ABR you inject e.g. default route into access IGP domain. ABR has /32 > LDP FECs, and advertises this /32 FECs in LDP (but not in IGP) downstream > into access domain. In access domain, LDP readvertises hop-by-hop these /32 > LDP FECs, assigning the labels. > > It is typically used with LDP DoD. On the other hand, however, nothing > prevents you from having LDP policy on ABR to inject into access domain only > specific /32 LDP FECs. Thanks Krzysztof, that was my understanding from the Juniper link I provided and the RFC, but it's still nice to have my understanding clarified by someone else. After reading the above RFCs I see that the specific use case for this feature is when using LDP in Downstream on Demand mode, although that isn't actually called out in RFC5283 anywhere or the Juniper documentation. I was thinking in DU mode in my head :) In DU mode, an agg node will advertise all labels to the access node. If the access node has say 10.0.0.0/22 summary route (an example range loopback IPs are assigned from) and RFC5283 enabled, and the agg node advertises 1024 /32 IPv4 FEC labels (one for each loopback assuming 1000 PEs exist) the access node will keep all 1000 labels even if it only needs a few of them, matching them against the summary route. This is the default LDP DU behaviour unless we create horrible per-LDP neighbour policies on the agg node that only allow the labels for the exact loopbacks that access node needs to reach. So relaxing the LDP exact match rules is kind of useless for LDP DU. In LDP DoD mode, the access nodes only request the label mappings for the labels they need, so no need for per-LDP neighbour policies, but we would still need per-LDP neighbour IP routing policies to only advertise the /32 loopback IPs that neighbor needs in the IGP, unless we use RFC5283 and advertise a summary route (or install a static summary route). Cheers, James. _______________________________________________ juniper-nsp mailing list juniper-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/juniper-nsp
