pyats-routing（皮亚茨路由）

Routing Protocol Analysis

Routing Table Analysis

Always start here. The routing table is the source of truth for forwarding decisions.

Full Routing Table

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip route"}'

Per-Protocol Routes

# OSPF routes only
PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip route ospf"}'

# BGP routes only
PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip route bgp"}'

# Connected and static
PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip route connected"}'

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip route static"}'

VRF Routes

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip route vrf MGMT"}'

Analysis checklist:

• Route source codes: C (connected), S (static), O (OSPF), O IA (OSPF inter-area), O E1/E2 (OSPF external), B (BGP), D (EIGRP), D EX (EIGRP external)
• Administrative distance and metric for each route
• Next-hop reachability — is the next-hop IP actually reachable?
• Recursive lookups — routes pointing to next-hops resolved through other routes
• Equal-cost multipath (ECMP) — multiple next-hops for the same prefix
• Default route presence and source
• Unexpected route absence — if a prefix should be there but is not

OSPF Deep Dive

OSPF Process Overview

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip ospf"}'

Check: Router ID, areas configured, SPF run count (high = instability), reference bandwidth, stub/NSSA config, authentication.

OSPF Neighbors

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip ospf neighbor"}'

Neighbor state analysis:

• FULL — Healthy, full adjacency
• FULL/DR or FULL/BDR — Normal on broadcast/NBMA networks
• FULL/DROTHER — Normal on broadcast/NBMA (non-DR/BDR)
• 2WAY/DROTHER — Normal, two DROTHERs don't form full adjacency
• INIT — One-way communication only → check MTU, ACLs, authentication
• EXSTART/EXCHANGE — Stuck in database exchange → MTU mismatch (most common), OSPF area mismatch, authentication
• LOADING — Stuck loading LSAs → database corruption, memory issues
• DOWN — No hello packets → interface down, ACL blocking, hello/dead timer mismatch

Common OSPF problems and their symptoms:

OSPF Interfaces

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip ospf interface"}'

Check per interface: Area assignment, network type (broadcast/point-to-point/NBMA), cost, hello/dead timers, DR/BDR election, authentication type, passive status.

OSPF Database (LSDB)

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip ospf database"}'

LSA types to understand:

• Type 1 (Router LSA) — Every router generates one per area
• Type 2 (Network LSA) — DR generates on broadcast/NBMA segments
• Type 3 (Summary LSA) — ABR advertises between areas
• Type 4 (ASBR Summary) — ABR advertises ASBR reachability
• Type 5 (External LSA) — ASBR redistributes external routes
• Type 7 (NSSA External) — External routes in NSSA areas (converted to Type 5 at ABR)

Red flags in LSDB:

• Rapidly incrementing sequence numbers → LSA flooding loop
• Type 5 LSAs in stub area → misconfiguration
• Missing Type 3 LSAs for expected inter-area prefixes → ABR filtering or area mismatch
• Duplicate Router IDs → same RID on two routers

BGP Deep Dive

BGP Summary

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip bgp summary"}'

Check: Local AS, router ID, table version, total paths/best paths, per-neighbor state.

Neighbor state column meaning:

• Number (e.g., 5) → Established, number = received prefixes
• Idle → Not configured correctly, or administratively shut
• Idle (Admin) → neighbor shutdown configured
• Active → TCP connection failing → check reachability, TTL, ACLs
• Connect → TCP SYN sent, no response
• OpenSent → TCP connected, waiting for OPEN reply
• OpenConfirm → OPEN received, waiting for KEEPALIVE
• Established → Healthy

BGP Neighbors Detail

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip bgp neighbors"}'

Deep analysis per neighbor:

• BGP state, uptime, last reset reason
• Messages sent/received (OPEN, UPDATE, KEEPALIVE, NOTIFICATION)
• Hold time and keepalive interval
• Address families negotiated
• Route-map/filter-list/prefix-list applied (inbound/outbound)
• Next-hop-self, soft-reconfiguration, route-reflector-client status
• Notification messages — decode the error code/subcode

Common BGP problems:

BGP Table

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip bgp"}'

BGP best path selection order (memorize this):

1. Highest Weight (Cisco proprietary, local to router)
2. Highest Local Preference (iBGP, default 100)
3. Locally originated (network/redistribute/aggregate)
4. Shortest AS-path
5. Lowest Origin (IGP < EGP < Incomplete)
6. Lowest MED (from same neighbor AS only)
7. eBGP over iBGP
8. Lowest IGP metric to next-hop
9. Oldest route (for eBGP)
10. Lowest router ID
11. Lowest neighbor IP

EIGRP Analysis

EIGRP Neighbors

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip eigrp neighbors"}'

Check: Hold timer (resetting to max means hellos received), uptime, SRTT, RTO, Q count (should be 0 — non-zero means retransmission queue backed up).

EIGRP Topology

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip eigrp topology"}'

DUAL states:

• Passive (P) → Route is stable, normal
• Active (A) → Route in active query state → DUAL is searching for a feasible successor → if stuck, SIA (Stuck In Active) will kill the neighbor

EIGRP metric components (classic): Bandwidth, Delay, Reliability, Load, MTU (only BW and delay used by default).

EIGRP metric components (wide/named mode): Throughput, Latency, Reliability, Load, MTU, Extended attributes.

Redistribution Audit

When multiple routing protocols are in use, check redistribution points:

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip protocols"}'

Redistribution checklist:

• Is redistribution mutual (two-way)? Risk of routing loops
• Are route-maps/prefix-lists applied to redistribution? They should be
• Are metrics set correctly on redistribution? (seed metric for EIGRP, metric-type for OSPF)
• Is there a risk of suboptimal routing through the redistribution boundary?
• Administrative distance tuning — are AD values set to prefer the right protocol?

Route Filtering Verification

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show route-map"}'

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip prefix-list"}'

Convergence Validation

After any routing change, verify convergence:

1. Check all expected neighbor adjacencies are FULL/Established
2. Verify the routing table has all expected prefixes
3. Ping across the network from the device to validate data plane
4. Check logs for any protocol events during the change
5. Compare route counts before and after

# Verify route count
PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_show_command '{"device_name":"R1","command":"show ip route summary"}'