# lab03-ISIS-CLOS ### Task Underlay. IS-IS Set up IS-IS in the underlay network to establish IP connectivity between all network devices. ### Network diagram ![stand-plan](https://content.gitbook.com/content/t770ZYQYIfz1HzwklrwS/blobs/Gsm1lIheezz6NEBYj1YN/stand-plan.png) The lab is built using the following role-based device mapping host- linux, leaf - frr, spine - arista ### Underlay IP Address Allocation • Underlay addressing follows the format 10.x.y.z, where: ⁠◦ x = Data Center ID ⁠◦ y = Spine switch ID ⁠◦ z = Sequential host address per leaf connection • Host addressing uses the 172.16.x.z/24 format, where: ⁠◦ x = Leaf switch ID ⁠◦ z = Sequential host address ⁠◦ Each leaf switch uses .1 as its own IP in the corresponding subnet • Loopback addressing uses 192.168.a.b/32, where: ⁠◦ a = 1 for spine switches ⁠◦ a = 2 for leaf switches ⁠◦ b = Spine or leaf ID (assigned sequentially) • IPv6 addressing uses fd00::\[IPv4] Interconnect ipv4 ipv6 | Device A | Interface A | IPv4 A | IPv6 A | Device B | Interface B | IPv4 B | IPv6 B | | -------- | ----------- | ------------- | -------------------- | -------- | ----------- | ------------- | -------------------- | | Spine-1 | Eth1 | 10.1.1.0/31 | fd00::10:1:1:0/127 | Leaf-1 | Eth8 | 10.1.1.1/31 | fd00::10:1:1:1/127 | | Spine-1 | Eth2 | 10.1.1.2/31 | fd00::10:1:1:2/127 | Leaf-2 | Eth8 | 10.1.1.3/31 | fd00::10:1:1:3/127 | | Spine-1 | Eth3 | 10.1.1.4/31 | fd00::10:1:1:4/127 | Leaf-3 | Eth8 | 10.1.1.5/31 | fd00::10:1:1:5/127 | | Spine-2 | Eth2 | 10.1.2.0/31 | fd00::10:2:1:0/127 | Leaf-1 | Eth9 | 10.1.2.1/31 | fd00::10:2:1:1/127 | | Spine-2 | Eth2 | 10.1.2.2/31 | fd00::10:2:1:2/127 | Leaf-2 | Eth9 | 10.1.2.3/31 | fd00::10:2:1:3/127 | | Spine-2 | Eth3 | 10.1.2.4/31 | fd00::10:2:1:4/127 | Leaf-3 | Eth9 | 10.1.2.5/31 | fd00::10:2:1:5/127 | | Host-1 | Eth1 | 172.16.1.2/24 | fd00::172:16:1:2/116 | Leaf-1 | Eth1 | 172.16.1.1/24 | fd00::172:16:1:1/116 | | Host-2 | Eth1 | 172.16.2.2/24 | fd00::172:16:2:2/116 | Leaf-2 | Eth1 | 172.16.2.1/24 | fd00::172:16:2:1/116 | | Host-3 | Eth1 | 172.16.3.2/24 | fd00::172:16:3:2/116 | Leaf-3 | Eth1 | 172.16.3.1/24 | fd00::172:16:3:1/116 | | Host-4 | Eth1 | 172.16.4.2/24 | fd00::172:16:4:2/116 | Leaf-3 | Eth2 | 172.16.4.1/24 | fd00::172:16:4:1/116 | loopback | Device | Loopback ipv4 | loopback ipv6 | | ------- | ------------- | ----------------- | | Spine-1 | 192.168.1.1 | fd00::192:168:1:1 | | Spine-2 | 192.168.1.2 | fd00::192:168:1:2 | | Leaf-1 | 192.168.2.1 | fd00::192:168:2:1 | | Leaf-2 | 192.168.2.2 | fd00::192:168:2:2 | | Leaf-3 | 192.168.2.3 | fd00::192:168:2:3 | isis.net is configured manually. System id derived from loopback IP address, area id 1. Table net | Device | NET | | ------- | ------------------------- | | Spine-1 | 49.0001.1921.6801.0001.00 | | Spine-2 | 49.0001.1921.6801.0002.00 | | Leaf-1 | 49.0001.1921.6802.0001.00 | | Leaf-2 | 49.0001.1921.6802.0002.00 | | Leaf-3 | 49.0001.1921.6802.0003.00 | {% hint style="info" %} Since task doesn't contain instructions for host IP addressing, and both leaf and spine nodes are implemented as routers, host IPs are assigned from separate subnets prior to overlay configuration. This ensures basic connectivity while keeping underlay and overlay roles clearly separated. {% endhint %} Once the overlay is deployed, we’ll place all hosts into a single subnet to emulate Layer 2 connectivity. ### Launching a lab in the Netlab **Netlab Usage Notes:** As in previous lab we need to enable bfd in frr.yml **Lab Notes:** \ Encountered issues while configuring BFD for IS-IS. After successfully enabling it manually, I concluded that Netlab’s documentation is inaccurate regarding the lack of BFD support for IS-IS on FRR instances. To enable BFD, I modified the module responsible for FRR IS-IS configuration: /`usr/local/lib/python3.10/dist-packages/netsim/ansible/templates/isis/frr.macro.j2` Netlab is supposed to be about zero manual configuration, even if manual edits are faster and simpler. However, I ran into a known FRR limitation - *Note: There will be just one BFD session per interface. If both IPv4 and IPv6 are configured, only an IPv6-based session is created.* *Note that there will be just one BFD session per interface. In case both IPv4 and IPv6 support are configured then just a IPv6 based session is created.* Checked the Arista EOS documentation and found that: *BFD is not supported for IPv6 IS-IS.* At this point, one could give up — but I suspected the lack of support was due to incomplete module implementation, not platform limitations. Manual testing confirmed that BFD for IS-IS over IPv6 works on EOS. To integrate it cleanly, I extended the EOS IS-IS module: `/usr/local/lib/python3.10/dist-packages/netsim/ansible/templates/isis/eos.macro.j2` Final caveat: EOS requires explicit protocol declaration for BFD. Since FRR runs in dual-stack mode, EOS must be explicitly told to use IPv6 for BFD sessions. File [Topology](https://github.com/aeangel/otus-DC-net/blob/main/lab03/topology.yml) For quick reference, here’s the inline listing:
topology.yml ```yml --- provider: clab module: [ isis] nodes: s1: device: eos id: 1 isis: instance: netlab net: 49.0001.1921.6800.1001.00 loopback: ipv4: 192.168.1.1/32 ipv6: fd00::192:168:1:1/128 s2: device: eos id: 2 isis: instance: netlab net: 49.0001.1921.6800.1002.00 loopback: ipv4: 192.168.1.2/32 ipv6: fd00::192:168:1:2/128 l1: device: frr id: 3 isis: instance: netlab net: 49.0001.1921.6800.2001.00 loopback: ipv4: 192.168.2.1/32 ipv6: fd00::192:168:2:1/128 l2: device: frr id: 4 isis: instance: netlab net: 49.0001.1921.6800.2002.00 loopback: ipv4: 192.168.2.2/32 ipv6: fd00::192:168:2:2/128 l3: device: frr id: 5 isis: instance: netlab net: 49.0001.1921.6800.2003.00 loopback: ipv4: 192.168.2.3/32 ipv6: fd00::192:168:2:3/128 h1: device: linux h2: device: linux h3: device: linux h4: device: linux links: #spine1-leaf1,2,3 - interfaces: - node: s1 ifname: eth1 isis: network_type: point-to-point bfd: ipv6: True ipv4: 10.1.1.0 ipv6: fd00::10:1:1:0 - node: l1 ifname: eth8 isis: network_type: point-to-point bfd: True ipv4: 10.1.1.1 ipv6: fd00::10:1:1:1 prefix: ipv4: 10.1.1.0/31 ipv6: fd00::10:1:1:0/127 - interfaces: - node: s1 ifname: eth2 ipv4: 10.1.1.2 ipv6: fd00::10:1:1:2 isis: network_type: point-to-point bfd: ipv6: True - node: l2 ifname: eth8 ipv4: 10.1.1.3 ipv6: fd00::10:1:1:3 isis: network_type: point-to-point bfd: True prefix: ipv4: 10.1.1.2/31 ipv6: fd00::10:1:1:2/127 - interfaces: - node: s1 ifname: eth3 ipv4: 10.1.1.4 ipv6: fd00::10:1:1:4 isis: bfd: ipv6: True - node: l3 ifname: eth8 ipv4: 10.1.1.5 ipv6: fd00::10:1:1:5 isis: bfd: True prefix: ipv4: 10.1.1.4/31 ipv6: fd00::10:1:1:4/127 #spine2-leaf1,2,3 - interfaces: - node: s2 ifname: eth1 ipv4: 10.1.2.0 ipv6: fd00::10:1:2:0 isis: network_type: point-to-point bfd: ipv6: true - node: l1 ifname: eth9 ipv4: 10.1.2.1 ipv6: fd00::10:1:2:1 isis: bfd: true prefix: ipv4: 10.1.2.0/31 ipv6: fd00::10:1:2:0/127 - interfaces: - node: s2 ifname: eth2 ipv4: 10.1.2.2 ipv6: fd00::10:1:2:2 isis: bfd: ipv6: true - node: l2 ifname: eth9 ipv4: 10.1.2.3 ipv6: fd00::10:1:2:3 isis: bfd: true prefix: ipv4: 10.1.2.2/31 ipv6: fd00::10:1:2:2/127 - interfaces: - node: s2 ifname: eth3 ipv4: 10.1.2.4 ipv6: fd00::10:1:2:4 isis: bfd: ipv6: true - node: l3 ifname: eth9 ipv4: 10.1.2.5 ipv6: fd00::10:1:2:5 isis: bfd: true prefix: ipv4: 10.1.2.4/31 ipv6: fd00::10:1:2:4/127 #host1 - interfaces: - node: h1 ifname: eth1 ipv4: 172.16.1.2 ipv6: fd00::172:16:1:2 - node: l1 ifname: eth1 isis: false ipv4: 172.16.1.1 ipv6: fd00::172:16:1:1 prefix: ipv4: 172.16.1.0/24 ipv6: fd00::172:16:1:0/116 #host2 - interfaces: - node: h2 ifname: eth1 ipv4: 172.16.2.2 ipv6: fd00::172:16:2:2 - node: l2 ifname: eth1 isis: false ipv4: 172.16.2.1 ipv6: fd00::172:16:2:1 prefix: ipv4: 172.16.2.0/24 ipv6: fd00::172:16:1:0/116 #host3 - interfaces: - node: h3 ifname: eth1 ipv4: 172.16.3.2 ipv6: fd00::172:16:3:2 - node: l3 ifname: eth1 isis: false ipv4: 172.16.3.1 ipv6: fd00::172:16:3:1 prefix: ipv4: 172.16.3.0/24 ipv6: fd00::172:16:3:0/116 #host4 - interfaces: - node: h4 ifname: eth1 ipv4: 172.16.4.2 ipv6: fd00::172:16:4:2 - node: l3 ifname: eth2 isis: false ipv4: 172.16.4.1 ipv6: fd00::172:16:4:1 prefix: ipv4: 172.16.4.0/24 ipv6: fd00::172:16:4:0/116 ```
### Validating
spine-1 ```txt s1#show ip ro VRF: default Gateway of last resort is not set C 10.1.1.0/31 directly connected, Ethernet1 C 10.1.1.2/31 directly connected, Ethernet2 C 10.1.1.4/31 directly connected, Ethernet3 I L2 10.1.2.0/31 [115/20] via 10.1.1.1, Ethernet1 I L2 10.1.2.2/31 [115/20] via 10.1.1.3, Ethernet2 I L2 10.1.2.4/31 [115/20] via 10.1.1.5, Ethernet3 C 192.168.1.1/32 directly connected, Loopback0 I L2 192.168.1.2/32 [115/30] via 10.1.1.1, Ethernet1 via 10.1.1.3, Ethernet2 via 10.1.1.5, Ethernet3 I L2 192.168.2.1/32 [115/20] via 10.1.1.1, Ethernet1 I L2 192.168.2.2/32 [115/20] via 10.1.1.3, Ethernet2 I L2 192.168.2.3/32 [115/20] via 10.1.1.5, Ethernet3 s1#show ipv6 ro VRF: default C fd00::10:1:1:0/127 [0/0] via Ethernet1, directly connected C fd00::10:1:1:2/127 [0/0] via Ethernet2, directly connected C fd00::10:1:1:4/127 [0/0] via Ethernet3, directly connected I L2 fd00::10:1:2:0/127 [115/20] via fe80::a8c1:abff:fef4:6f56, Ethernet1 I L2 fd00::10:1:2:2/127 [115/20] via fe80::a8c1:abff:fe01:dde1, Ethernet2 I L2 fd00::10:1:2:4/127 [115/20] via fe80::a8c1:abff:fe7b:3d0c, Ethernet3 C fd00::192:168:1:1/128 [0/0] via Loopback0, directly connected I L2 fd00::192:168:1:2/128 [115/30] via fe80::a8c1:abff:fef4:6f56, Ethernet1 via fe80::a8c1:abff:fe01:dde1, Ethernet2 via fe80::a8c1:abff:fe7b:3d0c, Ethernet3 I L2 fd00::192:168:2:1/128 [115/20] via fe80::a8c1:abff:fef4:6f56, Ethernet1 I L2 fd00::192:168:2:2/128 [115/20] via fe80::a8c1:abff:fe01:dde1, Ethernet2 I L2 fd00::192:168:2:3/128 [115/20] via fe80::a8c1:abff:fe7b:3d0c, Ethernet3 s1#show bfd peers VRF name: default ------------------ DstAddr MyDisc YourDisc Interface/Transport Type LastUp LastDown LastDiag State ------------------------------- ---------------- ---------------- ------------------------- ------------ -------------------- -------------- ------------------- ----- fe80::a8c1:abff:fe60:94a3 2730906329 2680068865 Ethernet2(2177) normal 08/27/25 15:43 NA No Diagnostic Up fe80::a8c1:abff:fe88:9959 2530925411 1836350440 Ethernet3(2183) normal 08/27/25 15:16 NA No Diagnostic Up fe80::a8c1:abff:fe92:99c2 1861245626 1908179683 Ethernet1(2173) normal 08/27/25 15:16 NA No Diagnostic Up s1#show isis neighbors Instance VRF System Id Type Interface SNPA State Hold time Circuit Id netlab default l1 L2 Ethernet1 P2P UP 29 00 netlab default l2 L2 Ethernet2 P2P UP 30 00 netlab default l3 L2 Ethernet3 P2P UP 28 00 s1#show isis network topology IS-IS Instance: netlab VRF: default IS-IS IPv4 paths to level-2 routers System Id Metric IA Metric Next-Hop Interface SNPA s2 20 0 l1 Ethernet1 P2P l2 Ethernet2 P2P l3 Ethernet3 P2P l1 10 0 l1 Ethernet1 P2P l2 10 0 l2 Ethernet2 P2P l3 10 0 l3 Ethernet3 P2P IS-IS IPv6 paths to level-2 routers System Id Metric IA Metric Next-Hop Interface SNPA s2 20 0 l1 Ethernet1 P2P l2 Ethernet2 P2P l3 Ethernet3 P2P l1 10 0 l1 Ethernet1 P2P l2 10 0 l2 Ethernet2 P2P l3 10 0 l3 Ethernet3 P2P ```
spine-2 ```txt s2#show ip ro Gateway of last resort is not set I L2 10.1.1.0/31 [115/20] via 10.1.2.1, Ethernet1 I L2 10.1.1.2/31 [115/20] via 10.1.2.3, Ethernet2 I L2 10.1.1.4/31 [115/20] via 10.1.2.5, Ethernet3 C 10.1.2.0/31 directly connected, Ethernet1 C 10.1.2.2/31 directly connected, Ethernet2 C 10.1.2.4/31 directly connected, Ethernet3 I L2 192.168.1.1/32 [115/30] via 10.1.2.1, Ethernet1 via 10.1.2.3, Ethernet2 via 10.1.2.5, Ethernet3 C 192.168.1.2/32 directly connected, Loopback0 I L2 192.168.2.1/32 [115/20] via 10.1.2.1, Ethernet1 I L2 192.168.2.2/32 [115/20] via 10.1.2.3, Ethernet2 I L2 192.168.2.3/32 [115/20] via 10.1.2.5, Ethernet3 s2#show ipv6 ro VRF: default I L2 fd00::10:1:1:0/127 [115/20] via fe80::a8c1:abff:fe8b:1dd7, Ethernet1 I L2 fd00::10:1:1:2/127 [115/20] via fe80::a8c1:abff:fe10:3ceb, Ethernet2 I L2 fd00::10:1:1:4/127 [115/20] via fe80::a8c1:abff:fee5:14ed, Ethernet3 C fd00::10:1:2:0/127 [0/0] via Ethernet1, directly connected C fd00::10:1:2:2/127 [0/0] via Ethernet2, directly connected C fd00::10:1:2:4/127 [0/0] via Ethernet3, directly connected I L2 fd00::192:168:1:1/128 [115/30] via fe80::a8c1:abff:fe8b:1dd7, Ethernet1 via fe80::a8c1:abff:fe10:3ceb, Ethernet2 via fe80::a8c1:abff:fee5:14ed, Ethernet3 C fd00::192:168:1:2/128 [0/0] via Loopback0, directly connected I L2 fd00::192:168:2:1/128 [115/20] via fe80::a8c1:abff:fe8b:1dd7, Ethernet1 I L2 fd00::192:168:2:2/128 [115/20] via fe80::a8c1:abff:fe10:3ceb, Ethernet2 I L2 fd00::192:168:2:3/128 [115/20] via fe80::a8c1:abff:fee5:14ed, Ethernet3 s2#show bfd peers VRF name: default ----------------- DstAddr MyDisc YourDisc Interface/Transport Type LastUp LastDown LastDiag State ------------------------------- ---------------- ---------------- ------------------------- ------------ -------------------- -------------- ------------------- ----- fe80::a8c1:abff:fe10:3ceb 2399755991 2604022487 Ethernet2(2171) normal 08/27/25 15:16 NA No Diagnostic Up fe80::a8c1:abff:fe8b:1dd7 854137237 4290215108 Ethernet1(2169) normal 08/27/25 15:16 NA No Diagnostic Up fe80::a8c1:abff:fee5:14ed 1230089738 45823714 Ethernet3(2179) normal 08/27/25 15:16 NA No Diagnostic Up s2#show isis neighbors Instance VRF System Id Type Interface SNPA State Hold time Circuit Id netlab default l1 L2 Ethernet1 P2P UP 28 00 netlab default l2 L2 Ethernet2 P2P UP 28 00 netlab default l3 L2 Ethernet3 P2P UP 29 00 s2#show isis network topology IS-IS Instance: netlab VRF: default IS-IS IPv4 paths to level-2 routers System Id Metric IA Metric Next-Hop Interface SNPA s1 20 0 l1 Ethernet1 P2P l2 Ethernet2 P2P l3 Ethernet3 P2P l1 10 0 l1 Ethernet1 P2P l2 10 0 l2 Ethernet2 P2P l3 10 0 l3 Ethernet3 P2P IS-IS IPv6 paths to level-2 routers System Id Metric IA Metric Next-Hop Interface SNPA s1 20 0 l1 Ethernet1 P2P l2 Ethernet2 P2P l3 Ethernet3 P2P l1 10 0 l1 Ethernet1 P2P l2 10 0 l2 Ethernet2 P2P l3 10 0 l3 Ethernet3 P2P ```
#### Verify ping reachability to all device loopbacks from leaf-3
leaf-3 pings ```txt l3# ping l1 PING l1 (192.168.2.1): 56 data bytes 64 bytes from 192.168.2.1: seq=0 ttl=63 time=1.610 ms 64 bytes from 192.168.2.1: seq=1 ttl=63 time=0.901 ms 64 bytes from 192.168.2.1: seq=2 ttl=63 time=0.808 ms ^C --- l1 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 0.808/1.106/1.610 ms l3# ping l2 PING l2 (192.168.2.2): 56 data bytes 64 bytes from 192.168.2.2: seq=0 ttl=63 time=1.253 ms 64 bytes from 192.168.2.2: seq=1 ttl=63 time=0.875 ms 64 bytes from 192.168.2.2: seq=2 ttl=63 time=0.850 ms ^C --- l2 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 0.850/0.992/1.253 ms l3# ping s1 PING s1 (192.168.1.1): 56 data bytes 64 bytes from 192.168.1.1: seq=0 ttl=64 time=0.074 ms 64 bytes from 192.168.1.1: seq=1 ttl=64 time=0.098 ms 64 bytes from 192.168.1.1: seq=2 ttl=64 time=0.095 ms 64 bytes from 192.168.1.1: seq=3 ttl=64 time=0.092 ms 64 bytes from 192.168.1.1: seq=4 ttl=64 time=0.115 ms ^C --- s1 ping statistics --- 5 packets transmitted, 5 packets received, 0% packet loss round-trip min/avg/max = 0.074/0.094/0.115 ms l3# ping s2 PING s2 (192.168.1.2): 56 data bytes 64 bytes from 192.168.1.2: seq=0 ttl=64 time=0.103 ms 64 bytes from 192.168.1.2: seq=1 ttl=64 time=0.094 ms 64 bytes from 192.168.1.2: seq=2 ttl=64 time=0.173 ms 64 bytes from 192.168.1.2: seq=3 ttl=64 time=0.106 ms 64 bytes from 192.168.1.2: seq=4 ttl=64 time=0.111 ms ^C --- s2 ping statistics --- 5 packets transmitted, 5 packets received, 0% packet loss round-trip min/avg/max = 0.094/0.117/0.173 ms l3# ping ipv6 l1 PING l1 (fd00::192:168:2:1): 56 data bytes 64 bytes from fd00::192:168:2:1: seq=0 ttl=63 time=1.274 ms 64 bytes from fd00::192:168:2:1: seq=1 ttl=63 time=1.009 ms 64 bytes from fd00::192:168:2:1: seq=2 ttl=63 time=0.636 ms ^C --- l1 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 0.636/0.973/1.274 ms l3# ping ipv6 l2 PING l2 (fd00::192:168:2:2): 56 data bytes 64 bytes from fd00::192:168:2:2: seq=0 ttl=63 time=1.395 ms 64 bytes from fd00::192:168:2:2: seq=1 ttl=63 time=1.001 ms 64 bytes from fd00::192:168:2:2: seq=2 ttl=63 time=1.386 ms ^C --- l2 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 1.001/1.260/1.395 ms l3# ping ipv6 s1 PING s1 (fd00::192:168:1:1): 56 data bytes 64 bytes from fd00::192:168:1:1: seq=0 ttl=64 time=0.140 ms 64 bytes from fd00::192:168:1:1: seq=1 ttl=64 time=0.115 ms 64 bytes from fd00::192:168:1:1: seq=2 ttl=64 time=0.096 ms ^C --- s1 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 0.096/0.117/0.140 ms l3# ping ipv6 s2 PING s2 (fd00::192:168:1:2): 56 data bytes 64 bytes from fd00::192:168:1:2: seq=0 ttl=64 time=0.105 ms 64 bytes from fd00::192:168:1:2: seq=1 ttl=64 time=0.098 ms 64 bytes from fd00::192:168:1:2: seq=2 ttl=64 time=0.202 ms 64 bytes from fd00::192:168:1:2: seq=3 ttl=64 time=0.090 ms ^C --- s2 ping statistics --- 4 packets transmitted, 4 packets received, 0% packet loss round-trip min/avg/max = 0.090/0.123/0.202 ms ```
Device configuration files: [Spine-1](https://github.com/aeangel/otus-DC-net/blob/main/lab03/s1.cfg) [Spine-2](https://github.com/aeangel/otus-DC-net/blob/main/lab03/s2.cfg) [Leaf-1](https://github.com/aeangel/otus-DC-net/blob/main/lab03/l1.cfg) [Leaf-2](https://github.com/aeangel/otus-DC-net/blob/main/lab03/l2.cfg) [Leaf-3](https://github.com/aeangel/otus-DC-net/blob/main/lab03/l3.cfg)