Necessary cookies and storage support sign-in and learning. Optional Vercel analytics and campaign measurement stay off unless you accept. Rejecting won't affect courses or checkout.
Global Privacy Control is on. Optional analytics stays off.
FREE TOOL
Paste a Cisco IOS XE IPv4 prefix list and enter a route, such as 10.30.1.0/24. The tester checks the route against each entry in sequence order, using the entry's prefix and its ge and le length range, stops at the first entry that matches, and shows which entry decided and why. The test runs in this page, and the page does not send what you paste to a server. No account is required.
This tester runs in your browser and needs JavaScript turned on. The boxes stay locked until the page script loads, so the page cannot send anything you enter. If they stay locked, the script did not load. Turn on JavaScript or reload the page to use the tester.
The tester is ready. It runs in this page, and the page does not send what you enter to a server.
One row for each entry of the list, lowest sequence number first, with the lengths it matches and what the tester found.
| Line | Seq | Entry | Lengths matched | Result |
|---|
Each step shows the 32 bits in binary and dotted decimal. Network bits are shown in bold and host bits in normal weight where a prefix applies.
A prefix list filters routes, not packets. Routing features such as a route map or a BGP neighbor filter pass each route to the list, and the list permits or denies it. IOS evaluates the entries starting with the lowest sequence number and stops at the first entry that matches, so the rest of the list is not evaluated. A route that matches no entry is denied by an implicit deny at the end of the list, which the configuration does not show.
An entry such as "permit 172.16.0.0/12 ge 16 le 24" tests two things. The first 12 bits of the route must equal 172.16.0.0, and the route's own length must fall in the entry's range. The range comes from ge and le:
To practice, take the example list below and decide on paper what happens to 172.16.0.0/16, 172.20.1.0/25 and 10.40.1.0/24. Then paste it and test each route. The second route is the interesting one: it is inside 172.16.0.0/12 but too long for seq 10, so it falls through to the catch-all at seq 30.
ip prefix-list PL-GELE seq 10 permit 172.16.0.0/12 ge 16 le 24
ip prefix-list PL-GELE seq 20 deny 10.40.0.0/16 le 32
ip prefix-list PL-GELE seq 30 permit 0.0.0.0/0 le 32IOS XE accepts an entry only when length < ge <= le <= 32. We checked this on the same IOS XE 17.12.1 router the example output came from. The router accepted 10.0.0.0/8 ge 24 le 24, and it refused 10.0.0.0/24 le 24 with "% Invalid prefix range for 10.0.0.0/24, make sure: len < ge-value <= le-value". So ge can equal le, but ge and le must both be longer than the prefix length.
An entry with ge equal to le matches one route length. On that router, 10.0.0.0/8 ge 24 le 24 let 10.0.0.0/24, 10.1.1.0/24 and 10.1.2.0/24 through a route map and stopped the other five static routes: 10.0.0.0/25, 10.1.0.0/16, 10.1.1.128/25, 10.1.1.200/32 and 172.20.1.0/24. The tester evaluates these entries the same way.
The tester refuses an entry that breaks the rule and says which part: ge at or below the prefix length, le shorter than ge, le at or below the prefix length, or a value above 32. The router refuses the same entries, so a list that breaks the rule is not one you could have configured. Cisco's 17.16 command reference prints the rule as "length <ge ge-length <le le-length <= 32". That text has lost some of its markup, and it does not show whether each "<" was meant as "<=", so the rule on this page comes from the router.
The result depends on the whole list you pasted, and a prefix list is device configuration. This page never writes configuration to a link, so the tester has no share link and never writes the list or the route to the page's URL. Use Copy results to keep a record of a test.
The tester tests one IPv4 route against one list. It does not know which routing feature uses the list, and it does not model route maps, BGP or redistribution. It reads IPv4 lists only, with sequence numbers, in the three renderings captured from Cisco IOS XE 17.12.1 running as IOL on Cisco Modeling Labs. An entry whose network has bits set past its length is not evaluated, because the captured output shows no such entry. Other releases and platforms can print lists differently. The working shows the first 5 entries checked, and the table lists every entry.
Source: Cisco IOS XE 17.16 command reference, ip prefix-list, for evaluation order, exact match, the ge and le ranges and the implicit deny. It is the Catalyst 9500 reference; the captured output came from IOS XE 17.12.1 on IOL. The rule length < ge <= le <= 32 comes from that IOL router, which accepted and refused the entries quoted above.