# [SR-MPLS] LAB Segment Routing with SR-TE and PCE # **Lab topology** and sample configs for testing **Segment Routing with SR-TE and PCE** on Cisco IOS XE routers. --- ## 🖥️ Topology ```plaintext [ R1 ]---[ R2 ]---[ R3 ]---[ R4 ] | | |-------------------------| ``` * **R1:** PCC (client), Source * **R4:** Destination * **R2 & R3:** Transit * **Loopbacks:** * R1 = 1.1.1.1/32, SID 16001 * R2 = 2.2.2.2/32, SID 16002 * R3 = 3.3.3.3/32, SID 16003 * R4 = 4.4.4.4/32, SID 16004 --- ## 🔧 Common OSPF & SR Config (on all routers) ```plaintext hostname R1 ! interface Loopback0 ip address 1.1.1.1 255.255.255.255 ! interface Gig0/0 ip address 10.0.12.1 255.255.255.0 mpls ip ip ospf 1 area 0 ! router ospf 1 router-id 1.1.1.1 segment-routing mpls ! mpls traffic-eng ! segment-routing mpls global-block 16000 23999 connected-prefix-sid-map address 1.1.1.1/32 absolute-sid 16001 ``` Change IPs and SIDs accordingly for R2–R4. --- ## 🧠 On PCE Node (e.g., R2) ```plaintext pce segment-routing peer 1.1.1.1 source-address 2.2.2.2 lsr-id 2.2.2.2 capability pcc capability pce ! pcc-address-family ipv4 stateful-client ! pce-address-family ipv4 source-address 2.2.2.2 ``` --- ## 🧭 On PCC Node (R1) ```plaintext pce segment-routing pcc peer 2.2.2.2 source-address 1.1.1.1 ``` --- ## 🚀 Tunnel (SR-TE Policy on R1 to R4) ```plaintext interface Tunnel100 ip unnumbered Loopback0 tunnel mode mpls traffic-eng tunnel destination 4.4.4.4 tunnel mpls traffic-eng path-option 10 dynamic tunnel mpls traffic-eng autoroute announce segment-routing mpls ``` --- ## 📋 Verification * `show pce peer` * `show pce lsp` * `show segment-routing traffic-eng policy` * `show mpls forwarding-table` # More details ```plaintext [R1 - PCC] | (IGP + SR) | [R2 - PCE] / \ / \ [R3]----(IGP)----[R4] ``` ### Roles: * **R1 (PCC)**: Requests a path from the PCE. * **R2 (PCE)**: Computes the best SR-TE path based on constraints (e.g., low latency, bandwidth). * **R3 & R4**: Intermediate and destination routers. ### Traffic Flow: 1. R1 uses IGP (e.g., OSPF or IS-IS) with Segment Routing enabled to advertise and receive labels (SIDs). 2. R1, as PCC, sends a path computation request (PCEP) to R2. 3. R2, as PCE, computes a TE path using available topology and policy constraints. 4. R1 receives the path and installs it as an SR-TE policy. 5. Traffic follows the SR policy instead of IGP’s default shortest path. ### Benefits of SR-TE with PCE: * Centralized path computation (PCE). * Dynamic re-optimization when network state changes. * SLA-aware routing (e.g., avoid congested links or meet latency targets). * Supports automation via NETCONF/YANG or CLI. ## The configuration to include **bandwidth**, **affinity (link color)**, and **explicit path constraints** in Cisco IOS-XR. --- ### 🧱 Example Network Setup ```plaintext R1 -- R2 -- R3 -- R4 R1 = PCC (headend) R2 = PCE (central controller) R4 = destination Links: SR-MPLS enabled, OSPF/ISIS as IGP ``` --- ### 1️⃣ Add Affinity (Link Color) to Interfaces (on R2, R3) > Suppose you want traffic to use only "green" links. ```plaintext interface GigabitEthernet0/0/0/1 description Link to R3 (green) segment-routing forwarding affinity 0x2 ``` Here: * `affinity 0x2` marks the link as "green". * Affinity is a 32-bit bitmask — you define meanings separately. --- ### 2️⃣ Define Affinity Mapping (on PCE or router where policy is configured) ```plaintext segment-routing traffic-eng affinity-map green 0x2 ``` --- ### 3️⃣ Define SR-TE Policy with Constraints (on R1 — PCC) ```plaintext segment-routing traffic-eng policy SRTE-R1-R4 color 100 end-point ipv4 10.0.0.4 candidate-paths preference 100 constraints affinity include green bandwidth 1000000 ! in Kbps (1 Gbps) explicit segment-list R1-R2-R3-R4 ``` --- ### 4️⃣ Define Explicit Segment List (Optional for hard path pinning) ```plaintext segment-routing traffic-eng segment-list R1-R2-R3-R4 index 10 mpls label 16002 ! R2 SID index 20 mpls label 16003 ! R3 SID index 30 mpls label 16004 ! R4 SID ``` --- ### ✅ What This Does: * **Bandwidth**: Allocates bandwidth-aware paths via the PCE. * **Affinity**: Ensures only “green” tagged links are used. * **Explicit path**: You can pin the SR path manually using segment SIDs. Here is the full configuration for a Cisco SR-TE setup using a PCE-PCC model across four routers (R1 to R4). R1 is the PCC, R2 is the PCE, and R3/R4 are transit/destination nodes. * ```plaintext ! ! R1 Configuration (PCC) ! hostname R1 ! interface Loopback0 ip address 1.1.1.1 255.255.255.255 ! interface GigabitEthernet0/0 ip address 10.0.12.1 255.255.255.0 mpls ip ip ospf 1 area 0 ! interface GigabitEthernet0/1 ip address 10.0.14.1 255.255.255.0 mpls ip ip ospf 1 area 0 ! router ospf 1 router-id 1.1.1.1 network 10.0.12.0 0.0.0.255 area 0 network 10.0.14.0 0.0.0.255 area 0 network 1.1.1.1 0.0.0.0 area 0 segment-routing mpls ! mpls traffic-eng ! segment-routing mpls global-block 16000 23999 connected-prefix-sid-map address 1.1.1.1/32 absolute-sid 16001 ! pce segment-routing pcc peer 2.2.2.2 source-address 1.1.1.1 ! interface Tunnel100 ip unnumbered Loopback0 tunnel mode mpls traffic-eng tunnel destination 4.4.4.4 tunnel mpls traffic-eng path-option 10 dynamic tunnel mpls traffic-eng autoroute announce segment-routing mpls ! ! R2 Configuration (PCE) ! hostname R2 ! interface Loopback0 ip address 2.2.2.2 255.255.255.255 ! interface GigabitEthernet0/0 ip address 10.0.12.2 255.255.255.0 mpls ip ip ospf 1 area 0 ! interface GigabitEthernet0/1 ip address 10.0.23.1 255.255.255.0 mpls ip ip ospf 1 area 0 ! router ospf 1 router-id 2.2.2.2 network 10.0.12.0 0.0.0.255 area 0 network 10.0.23.0 0.0.0.255 area 0 network 2.2.2.2 0.0.0.0 area 0 segment-routing mpls ! mpls traffic-eng ! segment-routing mpls global-block 16000 23999 connected-prefix-sid-map address 2.2.2.2/32 absolute-sid 16002 ! pce segment-routing peer 1.1.1.1 source-address 2.2.2.2 lsr-id 2.2.2.2 capability pcc capability pce ! pcc-address-family ipv4 stateful-client ! pce-address-family ipv4 source-address 2.2.2.2 ! ! R3 Configuration (Transit) ! hostname R3 ! interface Loopback0 ip address 3.3.3.3 255.255.255.255 ! interface GigabitEthernet0/0 ip address 10.0.23.2 255.255.255.0 mpls ip ip ospf 1 area 0 ! interface GigabitEthernet0/1 ip address 10.0.34.1 255.255.255.0 mpls ip ip ospf 1 area 0 ! router ospf 1 router-id 3.3.3.3 network 10.0.23.0 0.0.0.255 area 0 network 10.0.34.0 0.0.0.255 area 0 network 3.3.3.3 0.0.0.0 area 0 segment-routing mpls ! mpls traffic-eng ! segment-routing mpls global-block 16000 23999 connected-prefix-sid-map address 3.3.3.3/32 absolute-sid 16003 ! ! R4 Configuration (Destination) ! hostname R4 ! interface Loopback0 ip address 4.4.4.4 255.255.255.255 ! interface GigabitEthernet0/0 ip address 10.0.34.2 255.255.255.0 mpls ip ip ospf 1 area 0 ! interface GigabitEthernet0/1 ip address 10.0.14.2 255.255.255.0 mpls ip ip ospf 1 area 0 ! router ospf 1 router-id 4.4.4.4 network 10.0.34.0 0.0.0.255 area 0 network 10.0.14.0 0.0.0.255 area 0 network 4.4.4.4 0.0.0.0 area 0 segment-routing mpls ! mpls traffic-eng ! segment-routing mpls global-block 16000 23999 connected-prefix-sid-map address 4.4.4.4/32 absolute-sid 16004 ```