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cmd/tailscale: add "debug via" subcommand to do CIDR math for via ranges

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$ tailscale debug via 0xb 10.2.0.0/16
fd7a:115c:a1e0:b1a:0🅱️a02:0/112
$ tailscale debug via fd7a:115c:a1e0:b1a:0🅱️a02:0/112
site 11 (0xb), 10.2.0.0/16

Previously: 3ae701f0eb

This adds a little debug tool to do CIDR math to make converting between
those ranges easier for now.

Updates #3616

Change-Id: I98302e95d17765bfaced3ecbb71cbd43e84bff46
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2022-04-20 14:25:27 -07:00
committed by Brad Fitzpatrick
parent f74ee80abe
commit d413850bd7
2 changed files with 67 additions and 0 deletions
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16
net/tsaddr/tsaddr.go
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@@ -6,6 +6,8 @@
package tsaddr
import (
"encoding/binary"
"errors"
"sync"
"inet.af/netaddr"
@@ -280,3 +282,17 @@ func UnmapVia(ip netaddr.IP) netaddr.IP {
}
return ip
}
// MapVia returns an IPv6 "via" route for an IPv4 CIDR in a given siteID.
func MapVia(siteID uint32, v4 netaddr.IPPrefix) (via netaddr.IPPrefix, err error) {
if !v4.IP().Is4() {
return via, errors.New("want IPv4 CIDR with a site ID")
}
viaRange16 := TailscaleViaRange().IP().As16()
var a [16]byte
copy(a[:], viaRange16[:8])
binary.BigEndian.PutUint32(a[8:], siteID)
ip4a := v4.IP().As4()
copy(a[12:], ip4a[:])
return netaddr.IPPrefixFrom(netaddr.IPFrom16(a), v4.Bits()+64+32), nil
}