{"id":655,"date":"2018-10-29T21:06:33","date_gmt":"2018-10-29T21:06:33","guid":{"rendered":"http:\/\/feralpacket.org\/?p=655"},"modified":"2018-10-29T21:06:33","modified_gmt":"2018-10-29T21:06:33","slug":"ospf-sham-links-notes","status":"publish","type":"post","link":"https:\/\/feralpacket.org\/?p=655","title":{"rendered":"OSPF Sham Links Notes"},"content":{"rendered":"

OSPF Sham Links<\/span><\/p>\n

<\/p>\n

If the customer is using a\u00a0back door\u00a0link that is in area 0, then this link will always be preferred over the MPLS L3VPN connection<\/p>\n

\u00a0– The\u00a0back door\u00a0link updates type 1 LSAs<\/p>\n

\u00a0 \u00a0 \u00a0-> Intra-Area<\/p>\n

\u00a0– The MPLS L3VPN updates are<\/p>\n

\u00a0 \u00a0 \u00a0-> type 3 LSAs (Inter-Area) if the OSPF process-ids match<\/p>\n

\u00a0 \u00a0 \u00a0-> type 5 LSAs (External 2) if the OSPF process-ids do not match<\/p>\n

The solution is to change the MPLS L3VPN updates to type 1 LSAs<\/p>\n

\u00a0– Achieved by using a sham-link<\/p>\n

Configuration<\/span><\/p>\n

\u00a01. Create new loopback interfaces on the PE routers<\/p>\n

\u00a02. Associate the loopbacks with the VRF<\/p>\n

\u00a03. Advertise the loopbacks in the BGP address-family VRF<\/p>\n

\u00a0 \u00a0 \u00a0-> Do not advertise the loopbacks into the PE – CE OSPF process<\/p>\n

\u00a04. Create the sham-link in the VRF OSPF on the PE routers<\/p>\n

\u00a05. Increase the cost on the interface of the backdoor link<\/p>\n

Sham-link loopback interfaces must be \/32 bit<\/p>\n

R1(config)# int lo10<\/span><\/p>\n

\u00a0ip vrf forwarding c1b1<\/span><\/p>\n

\u00a0ip add 50.0.0.1 255.255.255.255<\/span><\/p>\n

router bgp 100<\/span><\/p>\n

\u00a0address-family ipv4 vrf c1b1<\/span><\/p>\n

\u00a0 network 50.0.0.1 mask 255.255.255.255<\/span><\/p>\n

router ospf 10 vrf c1b1<\/span><\/p>\n

\u00a0area 0 sham-link 50.0.0.1 50.0.0.2 cost 1<\/span><\/p>\n

\u00a0 \u00a0 \u00a0-> 50.0.0.2 is the loopback IP address on the other PE router<\/p>\n

R4(config)# int s0\/0<\/span><\/p>\n

\u00a0ip ospf cost 10000<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

OSPF Sham Links<\/p>\n","protected":false},"author":1,"featured_media":654,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[51,24,31,50],"class_list":["post-655","post","type-post","status-publish","format-standard","hentry","category-ccie","tag-mpls-l3vpn","tag-ospf","tag-published","tag-sham-link"],"_links":{"self":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/655","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=655"}],"version-history":[{"count":1,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/655\/revisions"}],"predecessor-version":[{"id":740,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/655\/revisions\/740"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/media\/654"}],"wp:attachment":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=655"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=655"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=655"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}