Date created: Wednesday, December 4, 2024 11:52:39 AM. Last modified: Friday, December 6, 2024 1:16:19 PM
Basic ISIS-SR FlexAlgo
Full Configs
Login details are: admin/admin
IS-IS key is: admin
This was tested using cEOS version 4.31.2F.
Topology
In this example two routers have two L3 links between them running ISIS-SR and FlexAlgo.
One link has a lower (more preferred) default ISIS metric. A TE metric is also configured on each link. Again, one link has a lower (more preferred) TE metric (the opposite link to the one with the more preferred default metric):
- pe1:et1 -> pe2:et1
- IS-IS metric: 10
- TE metric: 20
- pe1:et2 -> pe2:et2
- IS-IS metric: 20
- TE metric: 10
Default Routing
PE1 prefers the path to PE2's Loopback0 IP via the link with the lowest cost default IS-IS metric:
pe1#show isis interface brief IS-IS Instance: Gandalf VRF: default Interface Level IPv4 Metric IPv6 Metric Type Adjacency --------- ----- ----------- ----------- -------------- --------- Ethernet1 L2 10 10 point-to-point 1 Ethernet2 L2 20 20 point-to-point 1 Loopback0 L2 10 10 loopback (passive)
pe1#show isis neighbors
Instance VRF System Id Type Interface SNPA State Hold time Circuit Id
Gandalf default pe2 L2 Ethernet1 P2P UP 26 0F
Gandalf default pe2 L2 Ethernet2 P2P UP 22 11
pe1#show ip route 10.0.0.2/32 detail | beg 10.0.0.2
I L2 10.0.0.2/32 [115/20]
via 10.1.0.2, Ethernet1 pe1 -> pe2
FlexAlgo Routing
A FlexAlgo instance is also configured which uses the TE metric configured on each interface.
BGP is configured on both routers and the IP address from the Loopback10 interface on each router is advertised in BGP with a "color" extended community attached. The FlexAlgo instance is bound to the same colour (100).
The result is that lookups for the next-hop of these BGP routes uses the FlexAlgo calculated topology, and as a result, PE1 prefers the path to PE's2 Loopback10 IP via the path with the lowest TE metric (Ethernet2), not the lowest IS-IS default metric (Ethernet1):
pe1#show bgp ipv4 unicast 10.10.10.2/32 detail
BGP routing table information for VRF default
Router identifier 10.0.0.1, local AS number 65001
BGP routing table entry for 10.10.10.2/32
Paths: 1 available
Local
10.0.0.2 from 10.0.0.2 (10.0.0.2)
Origin IGP, metric 0, localpref 100, IGP metric 10, weight 0, tag 0
Received 00:07:57 ago, valid, internal, best
Extended Community: Color:CO(00):100
Rx SAFI: Unicast
Tunnel RIB eligible
Not advertised to any peer.
pe1#show ip route 10.10.10.2/32 detail | beg 10.10.10.2
B I 10.10.10.2/32 [200/0]
via 10.0.0.2/32, algorithm bandw, IS-IS FlexAlgo tunnel index 1
via TI-LFA tunnel index 0, label imp-null(3)
via 10.1.0.6, Ethernet2, label imp-null(3)
backup via 10.1.0.2, Ethernet1, label imp-null(3)
pe1#show isis flex-algo algorithm bandw
IS-IS Instance: Gandalf VRF: default
Algorithm Priority Level Advertiser
--------- -------- ----- ----------
bandw 237 L2 pe2
Parameters:
advertised
metric TE
color 100
Other advertisers: pe1
pe1#show isis flex-algo routers
IS-IS Instance: Gandalf VRF: default
Algorithm: bandw
Router Level Advertising Priority
------ ----- ----------- --------
pe1 L2 yes 237
pe2 L2 yes 237
pe1#show isis segment-routing prefix-segments
System ID: pe1 Instance: 'Gandalf'
SR supported Data-plane: MPLS SR Router ID: 10.0.0.1
Node: 4 Proxy-Node: 0 Prefix: 0 Total Segments: 4
Flag Descriptions: R: Re-advertised, N: Node Segment, P: no-PHP
E: Explicit-NULL, V: Value, L: Local
Segment status codes: * - Self originated Prefix, L1 - level 1, L2 - level 2, ! - SR-unreachable,
# - Some IS-IS next-hops are SR-unreachable
Prefix SID Type Flags System ID Level Protection Algorithm
------------------------- ----- ---------- ---------------------------- --------------- ----- ----------- -------------
* 10.0.0.1/32 1001 Node R:0 N:1 P:0 E:0 V:0 L:0 pe1 L2 unprotected SPF
* 10.0.0.1/32 2001 Node R:0 N:1 P:0 E:0 V:0 L:0 pe1 L2 unprotected bandw
10.0.0.2/32 1002 Node R:0 N:1 P:0 E:0 V:0 L:0 pe2 L2 link SPF
10.0.0.2/32 2002 Node R:0 N:1 P:0 E:0 V:0 L:0 pe2 L2 link bandw
pe1#show tunnel rib colored brief
Tunnel RIB: system-colored-tunnel-rib
Endpoint Color Tunnel Type Index(es) Tunnel Preference IGP Preference IGP Metric Metric Type
-------------- -------- ----------------- ------------ -------------------- ----------------- ------------- -----------
10.0.0.2/32 100 IS-IS FlexAlgo 1 65 115 10 metric
pe1#show tunnel rib brief
Tunnel RIB: system-tunnel-rib
Endpoint Tunnel Type Index(es) Tunnel Preference IGP Preference IGP Metric Metric Type
----------------- ------------------- --------------- ----------------------- -------------------- ---------------- -----------
10.0.0.2/32 IS-IS SR IPv4 1 65 115 20 metric
This is the full IS-IS database:
pe1#show isis database detail
Legend:
H - hostname conflict
U - node unreachable
IS-IS Instance: Gandalf VRF: default
IS-IS Level 2 Link State Database
LSPID Seq Num Cksum Life Length IS Received LSPID Flags
pe1.00-00 10 10629 64804 249 L2 0000.0000.0001.00-00 <>
LSP generation remaining wait time: 0 ms
Time remaining until refresh: 48420 s
NLPID: 0xCC(IPv4)
Hostname: pe1
Authentication mode: SHA Key id: 0 Length: 35
Area addresses: 49.0001
Interface address: 10.1.0.5
Interface address: 10.1.0.1
Interface address: 10.0.0.1
IS Neighbor : pe2.00 Metric: 10
IPv4 Neighbor Address: 10.1.0.2
IPv4 Interface Address: 10.1.0.1
Adj-sid: 100001 flags: [L V B] weight: 0x0
IS Neighbor : pe2.00 Metric: 20
IPv4 Neighbor Address: 10.1.0.6
IPv4 Interface Address: 10.1.0.5
Adj-sid: 100000 flags: [L V B] weight: 0x0
Reachability : 10.0.0.1/32 Metric: 10 Type: 1 Up
SR Prefix-SID: 1001 Flags: [N] Algorithm: 0
SR Prefix-SID: 2001 Flags: [N] Algorithm: 200
Router Capabilities: Router Id: 10.0.0.1 Flags: []
SR Local Block:
SRLB Base: 965536 Range: 65536
Area leader priority: 250 algorithm: 0
Maximum SID depth:
Base MPLS imposition (MSD type 1): 6
SR Capability: Flags: [I]
SRGB Base: 900000 Range: 65536
Algorithms: 0, 200
Flex Algo: Algorithm: 200 Metric: TE Metric (2) Calc: SPF (0) Prio: 237
pe2.00-00 10 26583 64804 249 L2 0000.0000.0002.00-00 <>
Remaining lifetime received: 65534 s Modified to: 65535 s
NLPID: 0xCC(IPv4)
Hostname: pe2
Authentication mode: SHA Key id: 0 Length: 35
Area addresses: 49.0001
Interface address: 10.1.0.6
Interface address: 10.0.0.2
Interface address: 10.1.0.2
IS Neighbor : pe1.00 Metric: 10
IPv4 Neighbor Address: 10.1.0.1
IPv4 Interface Address: 10.1.0.2
Adj-sid: 100001 flags: [L V B] weight: 0x0
IS Neighbor : pe1.00 Metric: 20
IPv4 Neighbor Address: 10.1.0.5
IPv4 Interface Address: 10.1.0.6
Adj-sid: 100000 flags: [L V B] weight: 0x0
Reachability : 10.0.0.2/32 Metric: 10 Type: 1 Up
SR Prefix-SID: 1002 Flags: [N] Algorithm: 0
SR Prefix-SID: 2002 Flags: [N] Algorithm: 200
Router Capabilities: Router Id: 10.0.0.2 Flags: []
SR Local Block:
SRLB Base: 965536 Range: 65536
Area leader priority: 250 algorithm: 0
Maximum SID depth:
Base MPLS imposition (MSD type 1): 6
SR Capability: Flags: [I]
SRGB Base: 900000 Range: 65536
Algorithms: 0, 200
Flex Algo: Algorithm: 200 Metric: TE Metric (2) Calc: SPF (0) Prio: 237 Previous page: vEOS Overview
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