{"action":"opened","issue":{"url":"https://api.github.com/repos/weaveworks/weave/issues/743","labels_url":"https://api.github.com/repos/weaveworks/weave/issues/743/labels{/name}","comments_url":"https://api.github.com/repos/weaveworks/weave/issues/743/comments","events_url":"https://api.github.com/repos/weaveworks/weave/issues/743/events","html_url":"https://github.com/weaveworks/weave/issues/743","id":81053325,"number":743,"title":"[ipam] have a default for -iprange","user":{"login":"bboreham","id":8125524,"avatar_url":"https://avatars.githubusercontent.com/u/8125524?v=3","gravatar_id":"","url":"https://api.github.com/users/bboreham","html_url":"https://github.com/bboreham","followers_url":"https://api.github.com/users/bboreham/followers","following_url":"https://api.github.com/users/bboreham/following{/other_user}","gists_url":"https://api.github.com/users/bboreham/gists{/gist_id}","starred_url":"https://api.github.com/users/bboreham/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/bboreham/subscriptions","organizations_url":"https://api.github.com/users/bboreham/orgs","repos_url":"https://api.github.com/users/bboreham/repos","events_url":"https://api.github.com/users/bboreham/events{/privacy}","received_events_url":"https://api.github.com/users/bboreham/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":0,"created_at":"2015-05-26T17:10:40Z","updated_at":"2015-05-26T17:10:40Z","closed_at":null,"body":"In general, we don't know what IP address ranges are in use on the target, so we ask the user to pick a free range.\r\n\r\nHowever, we could have a default, check whether that default is OK to use, and refuse to start if not.  The default might be 10.20.0.0/16; this is fairly large and steers clear of ranges like 10.2 which are used by virtualbox.\r\n\r\nWe can use the same approach that Docker does to check if a range is in use: see if there is any routing rule on the host that intersects the range.\r\n\r\nHaving just a single default is better than having several and picking the first one that is free, because the latter approach can lead to inconsistent choices across hosts which are much harder to diagnose."}}