{"id":753,"date":"2021-08-20T03:12:02","date_gmt":"2021-08-20T03:12:02","guid":{"rendered":"http:\/\/feralpacket.org\/?p=753"},"modified":"2021-08-20T03:12:02","modified_gmt":"2021-08-20T03:12:02","slug":"is-is-notes-2","status":"publish","type":"post","link":"https:\/\/feralpacket.org\/?p=753","title":{"rendered":"IS-IS Notes"},"content":{"rendered":"

IS-IS:<\/b><\/p>\n

– Link state routing protocol
\n     -> 0xFEFE
\n     -> 0x0800
\n– Connectionless Network Protocol (CLNP)
\n– Like an IP protocol suite in OSI model
\n     -> Router
\n          -> Intermediate System (IS)
\n     -> End host
\n          -> End System (ES)
\n     -> OSI protocol<\/p>\n

          -> Direct<\/p>\n

ly works over layer 2<\/p>\n

     -> Integrated IS-IS can have payload of IPv4 or IPv6<\/p>\n

IS-IS uses the following parameters<\/b>
\n– IS-IS Hello (IIH)
\n– Link State Packet (LSP)
\n     -> Database IS-IS
\n– Complete Sequence Number PDU (CSNP)
\n     -> A list of database entries
\n– Partial Sequence Number PDU (PSNP)
\n     -> A request to send LSPs<\/p>\n

<\/p>\n

Neighbor Formation<\/b><\/p>\n

 – IIH must match the following<\/p>\n

     -> Authentication<\/p>\n

     -> IS type<\/p>\n

     -> MTU<\/p>\n

     -> Priority<\/p>\n

     -> system-id \/ area-id<\/p>\n

Link can be point-to-point or multi-access<\/b><\/p>\n

 – Network types<\/p>\n

     -> Point-to-point<\/p>\n

     -> Broadcast<\/p>\n

          -> DIS is elected (Designated Intermediate System)<\/p>\n

          -> Highest priority selected<\/p>\n

          -> Highest Subnet Point of Attachment (SNPA)<\/p>\n

          -> MAC address (ethernet)<\/p>\n

          -> Frame-relay DLCI<\/p>\n

          -> Highest system-id<\/p>\n

          -> DIS election is pre-emptive<\/p>\n

SNAP Address<\/b><\/p>\n

 – Subnetwork Access Point<\/p>\n

 – 20 butes represented in HEX<\/p>\n

     -> Bytes 1 – 13<\/p>\n

          -> area-id<\/p>\n

     -> Bytes 14 – 20<\/p>\n

          -> Network Selector Field<\/p>\n

               -> Always equal to “00”<\/p>\n

A SNAP address with a NSEL part 0 Network Entity Title (NET) address<\/p>\n

     -> Must be an even number of bytes<\/p>\n

IS-IS Area and Backbone Network<\/b><\/p>\n

 – Level-1<\/p>\n

     -> Router configuration mode<\/p>\n

     -> Similar to a NSSA<\/p>\n

 – Level-2<\/p>\n

     -> Interface configuration mode<\/p>\n

     -> Similar to Area 0 routers<\/p>\n

 – Level-1-2<\/p>\n

 – The level decides which updates can be received<\/p>\n

 – Two routers can be in different areas and still form neighbors<\/p>\n

     -> This means IS-IS areas are per router, as opposed to OSPF which is area per-link<\/p>\n

<\/p>\n

<\/p>\n

All routers and links, by default, are Level-1-2<\/p>\n

 – Within an area, L-1-2 neighbors can be formed<\/p>\n

 – Between areas, only L-2 neighbors can be formed<\/p>\n

 – A consecutive set of Level-2 adjacencies is called a backbone, which may include several routers<\/p>\n

     -> The Level-2 adjacencies cannot be discontiguous<\/p>\n

 – The Level-1-2 router on the edge will send all Level-1 LSP with attached it set towards Level-1 routers<\/p>\n

IS-IS Data Flow Procedures<\/b><\/p>\n

 – Receive operation<\/p>\n

     -> Updates are received as LSP<\/p>\n

 – Update operation<\/p>\n

     -> Updates are sent as LSP<\/p>\n

 – Decision operation<\/p>\n

     -> SPF algorithm finding the best routes<\/p>\n

 – Forward operation<\/p>\n

     -> Create CEF table entries with the best routes<\/p>\n

IS-IS Metric<\/b><\/p>\n

 – Metric is cost<\/p>\n

 – Cost is constant 10 everywhere<\/p>\n

     -> No calculation<\/p>\n

 – By default, “narrow metric” is used<\/p>\n

     -> 6 bit<\/p>\n

     -> 1 – 63<\/p>\n

 – Can be changed to “wide metric”<\/p>\n

     -> 2^24<\/p>\n

 – \u201cWide metric\u201d is needed for MPLS TE<\/p>\n

IS-IS Topology<\/b><\/p>\n

 – Single topology<\/p>\n

     -> IPv4 and IPv6 address-families share the same path calculation<\/p>\n

     -> IPv4 and IPv6 has to be enabled on all interfaces configured for IS-IS<\/p>\n

          -> The interfaces doesn\u2019t necessarily need both IPv4 and \/ or IPv6 addresses configured<\/p>\n

 – Multi topology<\/p>\n

     -> IPv4 and IPv6 address-families calculate best paths independently<\/p>\n

     -> IPv4 and IPv6 configuration independent<\/p>\n

          -> Interfaces configured for IS-IS can have IPv4 enabled, IPv6 enabled, or both<\/p>\n

 – For IOS routers, the default configuration is single topology<\/p>\n

 – For XR routers, the default IPV6 configuration is multi topology<\/p>\n

<\/p>\n

Configuring IS-IS<\/b><\/p>\n

IOS Router<\/p>\n

(config)# router isis [<name>}<\/span><\/p>\n

     -> default name is NULL<\/p>\n

 net 49.001.0000.0000.1111.00<\/span><\/p>\n

int lo0<\/span><\/p>\n

 ip routing isis<\/span><\/p>\n

 ipv6 routing isis<\/span><\/p>\n

int fa0\/0<\/span><\/p>\n

 ip routing isis<\/span><\/p>\n

 ipv6 routing isis<\/span><\/p>\n

XR Router<\/p>\n

(config)# router isis <name><\/span><\/p>\n

 net 49.0001.0000.0000.1111.00<\/span><\/p>\n

     -> area: area 49.0001<\/p>\n

     -> system:  .0000.0000.1111<\/p>\n

     -> NSEL:  .00<\/p>\n

 int lo0<\/span><\/p>\n

  address-family ipv4 unicast<\/span><\/p>\n

  address-family ipv6 unicast<\/span><\/p>\n

 int g0\/0\/0\/0<\/span><\/p>\n

  address-family ipv4 unicast<\/span><\/p>\n

  address-family ipv6 unicast<\/span><\/p>\n

show clns neighbor<\/span><\/p>\n

show isis neighbor<\/span><\/p>\n

     -> “L1 L2 neighbors”<\/p>\n

IOS (Level type, interface)<\/p>\n

int e0\/0<\/span><\/p>\n

 isis circuit-type level-1<\/span><\/p>\n

XR (Level type, interface)<\/p>\n

router isis ABC<\/span><\/p>\n

 int g0\/0\/0\/0<\/span><\/p>\n

  circuit-type level-1<\/span><\/p>\n

IOS (Level type, entire router)<\/p>\n

router isis<\/span><\/p>\n

 is-type level-1<\/span><\/p>\n

XR (Level type, entire router)<\/p>\n

router isis ABC<\/p>\n

 is-type level-1<\/p>\n

IOS (Timers)<\/p>\n

int e0\/0<\/span><\/p>\n

 isis hello-interval <sec><\/span><\/p>\n

 isis hello-multiplier <count><\/span><\/p>\n

XR (Timers)<\/p>\n

router isis ABC<\/span><\/p>\n

 int g0\/0\/0\/0<\/span><\/p>\n

  hello-interval <sec><\/span><\/p>\n

  hello-multiplier <count><\/span><\/p>\n

IOS <\/p>\n

int e0\/0<\/span><\/p>\n

 isis priority <value><\/span><\/p>\n

     -> 0 – 127<\/span><\/p>\n

     -> 64 is default<\/span><\/p>\n

 isis metric <value> [ level-1 | level-2 ]<\/span><\/p>\n

 isis password <password><\/span><\/p>\n

 isis network { point-to-point | broadcast }<\/span><\/p>\n

Route Leaking<\/b><\/p>\n

 – Routes can be leaked from Level-1 to Level-2<\/p>\n

 – and visa versa<\/p>\n

On IOS Level-1-2 Router<\/p>\n

router isis<\/span><\/p>\n

 redistribute isis ip level-2 into level-1 { distribute-list <name> | route-map <name> }<\/span><\/p>\n

access-list <number> permit | deny <protocol> <source> <wildcard> <destination> <wildcard><\/span><\/p>\n

     -> network leaked – <source> <wildcard><\/p>\n

     -> subnet mask to match – <destination> <wildcard><\/p>\n

Scenario -> Leak the loopback of R3 to R1<\/p>\n

R2(config)# access-list 100 permit ip 3.3.3.3 0.0.0.0 255.255.255.255 0.0.0.0<\/span><\/p>\n

ip prefix-list ABC permit 3.3.3.3 255.255.255.255<\/span><\/p>\n

route-map LEAK<\/span><\/p>\n

 match ip add prefix-list ABC<\/span><\/p>\n

XR<\/p>\n

(config)# router-policy POLICY1<\/span><\/p>\n

 if destination in (3.3.3.3\/32)<\/span><\/p>\n

  pass<\/span><\/p>\n

  end if<\/span><\/p>\n

router isis ABC<\/span><\/p>\n

 address-family ipv4<\/span><\/p>\n

 propagate level-2 into level-1 route-policy POLICY1<\/span><\/p>\n

IOS<\/p>\n

(config)# mpls ip<\/span><\/p>\n

 mpls label protocol ldp<\/span><\/p>\n

 ip cef<\/span><\/p>\n

 int fa0\/0<\/span><\/p>\n

  mpls ip<\/span><\/p>\n

XR<\/p>\n

(config)# mpls ldp<\/span><\/p>\n

 int fa0\/0<\/span><\/p>\n

 int s0\/0<\/span><\/p>\n

 root<\/span><\/p>\n

 commit<\/span><\/p>\n

sh run mpls ldp<\/span><\/p>\n

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

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

Potential Problems<\/b><\/p>\n

Mismatched Level 1 and Level 2 interfaces<\/p>\n

Misconfigured NSAPs (NET)<\/p>\n

Duplicate system IDs<\/p>\n

Mismatched MTUsx<\/p>\n

Mismatched IP addresses and subnets<\/p>\n

Mismatched topologies (single vs. multi)<\/p>\n

Mismatched metrics (narrow vs. wide)<\/p>\n

 – Log Messages:<\/p>\n

      – TLV contents different, code 128<\/p>\n

          -> TLV 128 – IP Internal Reachability (narrow)<\/p>\n

      – TLV code mismatch<\/p>\n

      – TLV contents different, code 135<\/p>\n

          -> TLV 135 – Extended IP Reachability (wide)<\/p>\n

Verification (IOS): <\/b><\/p>\n

sh clns nei<\/span><\/p>\n

sh clns is-nei<\/span><\/p>\n

sh clns int<\/span><\/p>\n

sh isis nei<\/span><\/p>\n

sh isis spf-log<\/span><\/p>\n

sh isis database<\/span><\/p>\n

sh isis database detail<\/span><\/p>\n

     -> Use to determine whether single topology or multitopolgy is configured<\/p>\n

sh isis ip topology<\/span><\/p>\n

sh isis ipv6 topology<\/span><\/p>\n

sh clns<\/span><\/p>\n

sh clns protocol<\/span><\/p>\n

     -> Shows the metric types that are generated and accepted<\/p>\n

sh ip protocols<\/span><\/p>\n

sh ipv6 protocols<\/span><\/p>\n

sh isis topology<\/span><\/p>\n

sh clns nei detail<\/span><\/p>\n

sh clns int <int><\/span><\/p>\n

sh ip route isis<\/span><\/p>\n

sh ipv6 route isis<\/span><\/p>\n

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

ping 2.2.0.8 source lo0<\/span><\/p>\n

ping 2002:2:2::8 source lo0<\/span><\/p>\n

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

debug isis adj-packets<\/span><\/p>\n

debug isis update-packets<\/span><\/p>\n

debug spf-events<\/span><\/p>\n

Verification (XR):<\/b><\/p>\n

sh isis<\/span><\/p>\n

     -> Shows the metric types that are generated and accepted<\/p>\n

sh isis nei<\/span><\/p>\n

sh isis int bri<\/span><\/p>\n

sh isis spf-log<\/span><\/p>\n

sh isis database<\/span><\/p>\n

sh isis database detail<\/span><\/p>\n

     -> Use to determine whether single topology or multitopology is configured<\/p>\n

     -> Multitopology entries:<\/p>\n

  Metric: 10         MT (IPv6 Unicast) IPv6 2002:9:9::1\/128<\/p>\n

  Metric: 10         MT (IPv6 Unicast) IPv6 2002:9:9:11::\/64
\n  Metric: 10         MT (IPv6 Unicast) IPv6 2002:9:9:18::\/64<\/p>\n

     -> Singe topology entries:<\/p>\n

  Metric: 10         IPv6 2002:9:9::1\/128
\n  Metric: 10         IPv6 2002:9:9:11::\/64
\n  Metric: 10         IPv6 2002:9:9:18::\/64<\/p>\n

sh isis ipv4 topology<\/span><\/p>\n

sh isis ipv6 topology<\/span><\/p>\n

sh protocols<\/span><\/p>\n

sh protocols ipv6<\/span><\/p>\n

sh route isis<\/span><\/p>\n

sh route ipv6 isis<\/span><\/p>\n

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

ping 2.2.0.7 source 2.2.0.8<\/span><\/p>\n

ping 2002:2:2::7 source 2002:2:2::8<\/span><\/p>\n

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

IS-IS:<\/p>\n","protected":false},"author":1,"featured_media":749,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[9,31,10],"class_list":["post-753","post","type-post","status-publish","format-standard","hentry","category-ccie","tag-is-is","tag-published","tag-service-provider"],"_links":{"self":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/753","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=753"}],"version-history":[{"count":1,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/753\/revisions"}],"predecessor-version":[{"id":985,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/753\/revisions\/985"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/media\/749"}],"wp:attachment":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=753"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=753"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=753"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}