# Sorting ICE candidates by IPv6 in WebRtcServer
**URL:** https://mediasoup.discourse.group/t/sorting-ice-candidates-by-ipv6-in-webrtcserver/4522
**Category:** mediasoup libraries
**Created:** [August 30, 2022, 3:20pm UTC](https://mediasoup.discourse.group/t/sorting-ice-candidates-by-ipv6-in-webrtcserver/4522 "2022-08-30T15:20:09Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@jbaudanza](https://mediasoup.discourse.group/u/jbaudanza)
#### Post date: [August 30, 2022, 3:20pm UTC](https://mediasoup.discourse.group/t/sorting-ice-candidates-by-ipv6-in-webrtcserver/4522/1 "2022-08-30T15:20:09Z")
I’ve been migrating our `createWebRtcTransport` code from the `listenIps` api to the new `webRtcServer` api.
Our mediasoup process binds to both ipv6 and ipv4 IPs. When I construct the `listenIps` array, I prioritize either ipv4 or ipv6 candidates based on the IP address coming from the socketio signaling layer. I’ve found this has helped with some connectivity issues for some users inside of various kinds of IPv6 NATs. I think it probably speeds up the ICE process a bit too.
Since the WebRtcServer objects are created on startup, I’m not able to dynamically sort the candidate list like I can with the listenIps.
To get around this, I instantiate two WebRtcServer objects per worker: one sorted for ipv4 and one sorted for ivp6. I haven’t deployed this yet, but I think it should work. This approach means I need to bind to an extra port, but it’s not a big deal.
Ideally, I’d like to be able to use one WebRtcServer, and pass something like `preferIpv6` to `createWebRtcTransport`.
My questions:
1. Is there a better way to accomplish this candidate sorting?
2. Would a `preferIpv6` option be useful to anyone else? If so, I’m happy to put together a PR.
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### Author:  [@ibc](https://mediasoup.discourse.group/u/ibc)
#### Post date: [August 30, 2022, 3:43pm UTC](https://mediasoup.discourse.group/t/sorting-ice-candidates-by-ipv6-in-webrtcserver/4522/2 "2022-08-30T15:43:30Z")
If you pass the ips in the preferred order in the listenInfos array in worker.createWebRtcServer() it should have the same effect as before when you use listenIps array. If not, please report a bug in GH by showing how you pass those ips to both WebRtcTransport and WebRtcServer and how the resulting transport.iceCandidates array look in both cases.
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### Author:  [@jbaudanza](https://mediasoup.discourse.group/u/jbaudanza)
#### Post date: [August 30, 2022, 4:05pm UTC](https://mediasoup.discourse.group/t/sorting-ice-candidates-by-ipv6-in-webrtcserver/4522/3 "2022-08-30T16:05:10Z")
Yes, right. But I don’t know the preferred order when I create the WebRtcServer on startup. I only know the preferred order when a new client connects and requests a new transport. To get around this, I’m creating two WebRtcServers ahead of time, each sorted differently.
It seems we can manipulate the order of the candidates in the webRtcServer with the preferUdp and preferTcp flags. It would be convenient if I could also manipulate the order with `preferIpv4` / `preferIpv6`
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### Author:  [@jbaudanza](https://mediasoup.discourse.group/u/jbaudanza)
#### Post date: [September 28, 2022, 5:56am UTC](https://mediasoup.discourse.group/t/sorting-ice-candidates-by-ipv6-in-webrtcserver/4522/4 "2022-09-28T05:56:16Z")
The solution I came up with was to swap around the `priority` attribute in the `transport.iceCandidates` list before I pass them back to the client.
Is there any reason I shouldn’t do that? I can’t think of any.
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### Author:  [@ibc](https://mediasoup.discourse.group/u/ibc)
#### Post date: [September 28, 2022, 8:26am UTC](https://mediasoup.discourse.group/t/sorting-ice-candidates-by-ipv6-in-webrtcserver/4522/5 "2022-09-28T08:26:20Z")
That’s perfectly fine since mediasoup doesn’t care about which candidates the client prefers.