Linux Host Network Operations

Testbed Requirements

Linux hosts must be defined in the pyATS testbed with os: linux. See pyats-linux-system for the testbed YAML format.

How to Call

All commands use pyats_run_linux_command:

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-01","command":"<command>"}'

Commands

Interface Configuration

All Interfaces

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-01","command":"ifconfig"}'

Returns all interfaces with: IP address, netmask, broadcast, MAC address, MTU, RX/TX packets, RX/TX errors, RX/TX bytes, flags (UP/RUNNING/MULTICAST).

What to check:

• Interface UP/DOWN state — is the expected interface active?
• IP address correctness — does it match NetBox/Nautobot records?
• RX/TX errors — non-zero errors indicate physical or driver issues
• MTU — verify jumbo frames (9000) or standard (1500) as expected
• Dropped packets — may indicate buffer or rate-limit issues

Specific Interface

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-01","command":"ifconfig eth0"}'

Common interfaces to inspect:

• eth0 / ens192 — Primary management interface
• docker0 — Docker bridge network
• lo — Loopback (verify 127.0.0.1)
• bond0 — NIC bonding/teaming
• vlan100 — VLAN sub-interface
• tun0 / wg0 — VPN tunnel interfaces
• br-* — Docker/bridge networks

Routing Tables

Full Routing Table (All Tables)

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-01","command":"ip route show table all"}'

Returns routes from ALL routing tables — main, local, custom policy tables. This is the most comprehensive route view on a Linux host.

What to check:

• Default gateway present and correct
• Expected subnets reachable via correct interfaces
• Policy routing tables (table 100, table 200, etc.) configured correctly
• No blackhole or unreachable routes (unless intentional)
• Metric values — lower metric = preferred path

Legacy Route Command

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-01","command":"route"}'

Legacy route command — shows the kernel IP routing table (main table only). Prefer ip route show table all for complete view.

Route with Flags

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-01","command":"route -n"}'

The -n flag shows numeric addresses (no DNS resolution). Other useful flags:

• route -n — Numeric output (faster, no DNS dependency)
• route -e — Extended information (like netstat -r)

Network Connections

Routing Table via netstat

PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-01","command":"netstat -rn"}'

netstat -rn shows the kernel routing table in numeric format. Equivalent to route -n but with netstat-style output columns: Destination, Gateway, Genmask, Flags, MSS, Window, irtt, Iface.

Route flags:

• U — Route is up
• G — Route uses a gateway
• H — Target is a host (not a network)
• D — Created by ICMP redirect
• M — Modified by ICMP redirect

---

Workflows

1. Linux Network Health Check

pyats_list_devices → identify Linux hosts in testbed
→ pyats_run_linux_command(host, "ifconfig") → check interface states
→ pyats_run_linux_command(host, "ip route show table all") → verify routing
→ pyats_run_linux_command(host, "netstat -rn") → cross-reference routes
→ Flag: interfaces down, missing routes, error counters > 0
→ Severity-sort → GAIT

2. Linux Network Audit

pyats_list_devices → identify all Linux hosts
→ pyats_run_linux_command per host ("ifconfig") → collect interface data
→ Cross-reference IPs with NetBox/Nautobot IPAM → flag drift
→ pyats_run_linux_command per host ("ip route show table all") → collect routes
→ Verify default gateways match expected values
→ GAIT

3. Multi-Host Routing Comparison

pyats_run_linux_command(host-1, "ip route show table all") → host 1 routes
→ pyats_run_linux_command(host-2, "ip route show table all") → host 2 routes
→ Compare: same subnets, same gateways, same metrics?
→ Flag asymmetric routing or missing routes
→ GAIT

4. Interface Error Investigation

pyats_run_linux_command(host, "ifconfig") → check all interfaces
→ Identify interfaces with non-zero RX/TX errors or drops
→ pyats_run_linux_command(host, "ifconfig eth0") → deep dive on problem interface
→ Correlate with network device interfaces (pyats-network show commands)
→ GAIT

5. Post-Change Network Verification

ServiceNow CR must be in Implement state
→ pyats_run_linux_command(host, "ifconfig") → verify interface state post-change
→ pyats_run_linux_command(host, "ip route show table all") → verify routes post-change
→ pyats_run_linux_command(host, "netstat -rn") → confirm routing table
→ Compare against pre-change baseline
→ GAIT

---

Parallel Operations

Run network checks across multiple Linux hosts concurrently:

# Host 1
PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-01","command":"ifconfig"}'

# Host 2
PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-02","command":"ifconfig"}'

# Host 3
PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_run_linux_command '{"device_name":"linux-host-03","command":"ifconfig"}'

---

Integration with Other Skills

Skill	Integration
pyats-network	Correlate Linux host interfaces with network device interfaces — verify end-to-end connectivity
pyats-routing	Compare Linux host routes with network device routing tables (OSPF, BGP, EIGRP)
pyats-linux-system	System-level commands (ps, docker, ls) complement network-level inspection
pyats-linux-vmware	VMware ESXi host networking (vSwitch, vmkernel) via vim-cmd
pyats-parallel-ops	pCall pattern for fleet-wide Linux network audits
pyats-troubleshoot	Linux host network data feeds into OSI-layer troubleshooting
netbox-reconcile	Cross-reference ifconfig IP/MAC data against NetBox IPAM and DCIM records
nautobot-sot	Same as NetBox — validate Linux host IP addresses against Nautobot
subnet-calculator	Verify subnet masks and CIDR notation from ifconfig output
gait-session-tracking	Every Linux network command logged in GAIT

---

Guardrails

• Always call pyats_list_devices first — verify Linux hosts exist in the testbed
• Read-only commands only — ifconfig, ip route show, netstat, route are all read-only
• No configuration changes — never use ip addr add, ip route add, ifconfig up/down, or iptables via this skill
• Gate network changes behind ServiceNow — if extending to write operations, require a Change Request
• Cross-reference with SoT — always compare discovered IPs and routes against NetBox/Nautobot
• Record in GAIT — every command execution must be logged