show ip route summary
Displays a summary of the IP routing table, including route counts, protocols, and memory usage, used to quickly assess the routing table size and composition.
Definition: show ip route summary is a Cisco IOS privileged exec command. Displays a summary of the IP routing table, including route counts, protocols, and memory usage, used to quickly assess the routing table size and composition.
Overview
The 'show ip route summary' command is a powerful tool in Cisco IOS that provides a concise yet comprehensive overview of the IP routing table. It displays the total number of routes, the number of routes per routing protocol (e.g., OSPF, EIGRP, BGP), the number of subnets, and the memory usage associated with the routing table. This command is essential for network engineers who need to quickly assess the size and composition of the routing table, especially in large-scale networks where routing tables can become massive. Understanding the routing table's composition helps in capacity planning, troubleshooting routing issues, and verifying that routing protocols are operating correctly.
The networking concept behind this command is the routing table itself, which is a data structure stored in a router's memory that contains routes to destination networks. Each route includes the next-hop address, outgoing interface, administrative distance, and metric. The routing table is built from directly connected networks, static routes, and dynamic routing protocols. The 'show ip route summary' command aggregates this information, giving a high-level view without the detail of individual routes. This is particularly useful when you need to know how many routes are being learned from each protocol, whether the routing table is approaching its maximum capacity, or how much memory is being consumed.
You would reach for this command over alternatives like 'show ip route' (which lists all routes in detail) when you need a quick snapshot rather than a full dump. For example, after configuring a new routing protocol or adding a large number of routes, you can use this command to verify that the expected number of routes is present. It is also useful during troubleshooting when you suspect a routing protocol is not exchanging routes correctly; a discrepancy in route counts can indicate a problem. Additionally, when monitoring memory usage, this command shows how much memory the routing table consumes, which is critical for routers with limited resources.
In the broader network troubleshooting workflow, 'show ip route summary' is often used early in the process to get a baseline. For instance, if users report connectivity issues, you might first check the routing table summary to see if routes are missing or if there are unexpected route counts. It can be correlated with 'show ip protocols' to verify that routing protocols are configured and exchanging routes, and with 'show memory' to check overall memory pressure. The command is available in privileged EXEC mode (enable mode) and does not affect the running configuration. It is a read-only command that can be run at any time without impacting router performance, though on very large routing tables, it may take a moment to compute the summary. The output is buffered, meaning it may not reflect real-time changes if the routing table is being updated rapidly; in such cases, you may need to run the command multiple times. There are no privilege level requirements beyond enable mode, making it accessible to most network operators.
show ip route summaryWhen to Use This Command
- Check the total number of routes and memory consumption before adding new routes.
- Verify that a specific routing protocol (e.g., OSPF) has installed the expected number of routes.
- Troubleshoot routing table bloat or high memory usage.
- Compare route counts across different routers to ensure consistency.
Command Examples
Basic summary of routing table
show ip route summaryIP routing table name is Default-IP-Routing-Table (0x0) IP routing table maximum-paths is 32 Route entry count: 12 Number of networks: 12 Number of paths: 12 Number of paths for nexthop recursion: 0 Number of paths for load sharing: 0 Number of paths for per-packet load sharing: 0 Number of networks with paths: 12 Protocol Routes Connected 3 Static 1 OSPF 8 EIGRP 0 BGP 0 IS-IS 0 Memory bytes consumed: 3600
The output shows the routing table name and maximum paths. 'Route entry count' is the total number of routes. 'Number of networks' and 'Number of paths' are typically equal for simple topologies. The protocol breakdown shows how many routes each protocol contributed. 'Memory bytes consumed' indicates the memory used by the routing table.
Summary with many routes
show ip route summaryIP routing table name is Default-IP-Routing-Table (0x0) IP routing table maximum-paths is 32 Route entry count: 1500 Number of networks: 1500 Number of paths: 1500 Number of paths for nexthop recursion: 0 Number of paths for load sharing: 0 Number of paths for per-packet load sharing: 0 Number of networks with paths: 1500 Protocol Routes Connected 5 Static 2 OSPF 1493 EIGRP 0 BGP 0 IS-IS 0 Memory bytes consumed: 450000
This example shows a large routing table with 1500 routes, mostly from OSPF. The memory consumption is 450,000 bytes. This could indicate a router in a large OSPF domain. High memory usage may require optimization or hardware upgrade.
Understanding the Output
The 'show ip route summary' command provides a high-level overview of the IP routing table. The first line indicates the routing table name (usually Default-IP-Routing-Table). 'IP routing table maximum-paths' shows the maximum number of equal-cost paths for load balancing (default 32).
'Route entry count' is the total number of routes. 'Number of networks' and 'Number of paths' are typically identical unless there are multiple paths to the same network. The protocol breakdown lists how many routes each routing protocol has installed.
'Memory bytes consumed' is the total memory used by the routing table entries. A sudden increase in route count or memory may indicate a routing loop or misconfiguration. Normal values depend on network size; for a small enterprise, a few hundred routes is typical, while large ISPs may have hundreds of thousands.
Configuration Scenarios
Verify OSPF Route Learning in a Multi-Area Network
A network engineer has configured OSPF across multiple areas and wants to confirm that inter-area routes are being learned correctly. The routing table should show a specific number of OSPF routes.
Topology
R1(Gi0/0)---10.0.12.0/30---(Gi0/0)R2(Gi0/1)---10.0.23.0/30---(Gi0/0)R3
R1 has loopback 1.1.1.1/32 in area 0, R3 has loopback 3.3.3.3/32 in area 1.Steps
- 1.Step 1: Enter privileged EXEC mode: Router> enable
- 2.Step 2: Run the summary command: Router# show ip route summary
- 3.Step 3: Examine the output for the 'ospf' line to see the number of OSPF routes. Expected: 2 OSPF routes (one intra-area and one inter-area).
- 4.Step 4: Compare with the total route count to ensure all expected routes are present.
! OSPF configuration on R1 Router(config)# router ospf 1 Router(config-router)# network 10.0.12.0 0.0.0.3 area 0 Router(config-router)# network 1.1.1.1 0.0.0.0 area 0 ! OSPF configuration on R2 Router(config)# router ospf 1 Router(config-router)# network 10.0.12.0 0.0.0.3 area 0 Router(config-router)# network 10.0.23.0 0.0.0.3 area 1 ! OSPF configuration on R3 Router(config)# router ospf 1 Router(config-router)# network 10.0.23.0 0.0.0.3 area 1 Router(config-router)# network 3.3.3.3 0.0.0.0 area 1
Verify: Run 'show ip route summary' on R2. Expected output snippet: 'ospf 2' under 'Routes by protocol'. Also run 'show ip route ospf' to see the actual routes.
Watch out: Ensure that OSPF areas are correctly configured; a misconfiguration can lead to routes being learned as inter-area instead of intra-area, affecting route counts.
Monitor Routing Table Memory Usage After Adding BGP Routes
After establishing a BGP peering with an ISP, the network engineer wants to check how much memory the new BGP routes consume and ensure the router has sufficient memory.
Topology
R1(Gi0/0)---192.168.1.0/30---(Gi0/0)ISP-Router
R1 has loopback 10.0.0.1/32.Steps
- 1.Step 1: Enter privileged EXEC mode: Router> enable
- 2.Step 2: Run the summary command: Router# show ip route summary
- 3.Step 3: Look at the 'Memory' section for 'Total memory used by routing table' and note the value.
- 4.Step 4: Compare with the number of BGP routes listed under 'bgp' in the 'Routes by protocol' section.
- 5.Step 5: Run 'show memory' to check overall memory usage and ensure the router is not under memory pressure.
! BGP configuration on R1 Router(config)# router bgp 65001 Router(config-router)# neighbor 192.168.1.2 remote-as 65000 Router(config-router)# network 10.0.0.1 mask 255.255.255.255
Verify: Run 'show ip route summary' and look for 'bgp' entry. Expected: 'bgp 100000' if 100,000 routes are received. Also check 'Memory' section for memory usage.
Watch out: BGP routes may not appear if the BGP session is not established or if the network statement is missing. Always verify BGP peering with 'show ip bgp summary'.
Troubleshooting with This Command
When using 'show ip route summary' for troubleshooting, the first step is to understand what healthy output looks like. A healthy routing table summary will show a reasonable number of routes per protocol, consistent with the network design. For example, in a small OSPF network, you might see 10 OSPF routes and 5 connected routes. The memory usage should be within expected limits for the router platform. Problem indicators include an unexpectedly high or low number of routes for a given protocol, a sudden increase in memory usage, or routes appearing under unexpected protocols.
Focus on the 'Routes by protocol' section. If you see routes under 'unknown' or 'other', that could indicate a misconfiguration or a bug. If the total number of routes is much higher than expected, it might indicate a routing loop or a route redistribution issue. Conversely, if routes are missing, check the protocol-specific counts. For example, if OSPF routes are missing, verify OSPF neighbor adjacencies with 'show ip ospf neighbor'. If BGP routes are missing, check BGP peering with 'show ip bgp summary'.
The 'Memory' section is critical for diagnosing memory pressure. If the routing table memory usage is high, the router may drop routes or experience performance issues. Compare the memory usage with the router's total memory (from 'show memory'). A common symptom is the router running out of memory, which can cause routing protocols to fail or the router to crash. If memory usage is high, consider summarizing routes or using route filtering to reduce the table size.
A step-by-step diagnostic flow: 1) Run 'show ip route summary' and note the total routes and per-protocol counts. 2) Compare with a baseline from a known good state. 3) If counts are off, drill down with 'show ip route [protocol]' to see specific routes. 4) Check routing protocol status with 'show ip protocols' and 'show ip ospf neighbor' or 'show ip bgp summary'. 5) If memory is high, run 'show memory' and 'show processes memory' to identify which process is consuming memory. 6) Correlate with 'show ip cache flow' if using CEF to see if CEF tables are also large.
This command can be correlated with 'show ip route' to get details of specific routes, and with 'show ip route count' (if available) to get a quick count without the summary. In troubleshooting scenarios, it is often the first command to run after noticing connectivity issues or after making routing changes. It provides a quick sanity check that the routing table is populated as expected.
CCNA Exam Tips
CCNA exam may ask you to identify which protocol contributed the most routes from the summary output.
Know that the 'maximum-paths' value can be changed with the 'maximum-paths' command under router configuration.
The exam might test that 'show ip route summary' does not show individual routes; use 'show ip route' for that.
Be aware that memory consumption is in bytes; a high value may indicate a need for route summarization.
Common Mistakes
Confusing 'route entry count' with 'number of networks' — they are usually the same but can differ with multiple paths.
Assuming the memory value is in kilobytes or megabytes — it is always bytes.
Forgetting that static routes and connected routes are also counted in the protocol breakdown.
show ip route summary vs show ip route
Both commands display IP routing table information, but they serve different purposes: 'show ip route summary' provides a high-level overview of route counts and memory usage, while 'show ip route' lists all routes with full details. They are often confused because both are used to assess routing table content, yet the summary is more for capacity planning and protocol distribution checks.
| Aspect | show ip route summary | show ip route |
|---|---|---|
| Scope | Aggregate counts and memory statistics | Individual route entries with next-hops |
| Output detail | Summary lines with protocol totals and memory | Full route entries with AD, metric, interface |
| Memory usage | Shows routing table memory consumption | Does not include memory information |
| Typical use case | Quick health check of routing table size and protocol balance | Troubleshooting specific route reachability or path selection |
| Protocol breakdown | Lists route counts per protocol (connected, static, OSPF, etc.) | Shows protocol in each route entry but no aggregated counts |
Use 'show ip route summary' when you need a fast assessment of routing table size, memory usage, and route distribution among protocols.
Use 'show ip route' when you need detailed information about specific routes, including next-hop addresses, interfaces, administrative distances, and metrics for troubleshooting or verification.
Platform Notes
In IOS-XE (e.g., Catalyst 9000 switches), the 'show ip route summary' command is available and produces similar output, but the memory usage fields may differ slightly. For example, IOS-XE may show 'Memory: 12345 bytes used, 67890 bytes free' while classic IOS shows 'Memory: 12345 bytes used'. The command syntax is identical.
In NX-OS (e.g., Nexus switches), the equivalent command is 'show ip route summary' as well, but the output format is different. NX-OS provides a more detailed breakdown, including per-VRF summaries. For example, 'show ip route summary vrf all' shows routing table summary for all VRFs.
In ASA firewalls, the command 'show route' provides a summary but not as detailed; there is no direct equivalent. ASA uses 'show route' to display the routing table, and you can use 'show route | grep -c' to count routes, but there is no built-in summary command. In IOS-XR, the command is 'show route summary' (without 'ip'), and it provides a comprehensive summary including route counts per protocol and memory usage.
The output is more verbose and includes per-protocol details. Between IOS versions, the command has remained largely consistent from 12.x to 16.x, though newer versions may include additional fields like 'Routes by protocol' for newer protocols like IS-IS. Always check the specific IOS documentation for your version, as minor variations exist.
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