> For the complete documentation index, see [llms.txt](https://ccie-sp.gitbook.io/ccie-spv5.1-labs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ccie-sp.gitbook.io/ccie-spv5.1-labs/labs/ldp/ldp-implicit-withdraw.md). # LDP Implicit Withdraw Load **isis.cfg** ``` #IOS-XE config replace flash:isis.cfg #IOS-XR configure load bootflash:isis.cfg commit replace y ``` * Configure LDP between R1 and R2 using interface commands * Configure R2 so that any existing FEC bindings with a new label are advertised and withdrawn using a single label mapping message ## Answer ``` #R1 int giw.12 mpls ip #R2 int giw.12 mpls ip ! mpls ldp neighbor 1.1.1.1 implicit-withdraw ``` ## Explanation In IOS, the old method for advertising a new label for an existing FEC was to implicitly withdraw the label by simply advertising a new label for that FEC. This is similar to BGP’s behavior, in which a new Update for the same prefix from a peer is considered as “replacing” the existing route. This is why BGP AddPath functionality requires a path ID - to keep paths separate and not implement implicit withdraw. In IOS-XE, the new style for LDP was to first withdraw the label explicitly, and then advertise a new label binding. To restore the old method we can use the following command. This functionality does not appear to be supported on IOS-XR in version 6.x.x. ``` #IOS-XE mpls ldp neighbor 1.1.1.1 implicit-withdraw ``` To test this out, we can create a static label binding on R2. This allows us to easily change the label associated with the FEC. First we create a static route: ``` #R2 ip route 10.10.10.10 255.255.255.255 20.2.3.3 ``` R2 will advertise this FEC binding with a dynamic label to R1. Next we create a static label range on R2. ``` #R2 mpls label range 200 299 static 2000 2999 ``` We can now allocate a static local label for this FEC on R2. ``` #R2 mpls static binding ipv4 10.10.10.10 255.255.255.255 2001 ``` R2 has not yet configured implicit-withdraw for R1. On R1, we can see that R2 sends two messages: a withdraw and then a label mapping:

Next, we set R2 for implicit-withdraw, and change the local static label for the FEC: ``` #R2 mpls ldp neighbor 1.1.1.1 implicit-withdraw ! mpls static binding ipv4 10.10.10.10 255.255.255.255 2002 ``` On R1 we now see only the new mapping message. This is an implicit withdraw for the old binding, instead of an explicit withdraw as we saw before.