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net: disable RFC 6724 Rule 9 for IPv4 addresses 

Rule 9 arguably doesn't make sense for IPv4 addresses, and so far it
has only caused problems (#13283, #18518). Disable it until we hear
from users that actually want/need it.

Fixes #18518.

Change-Id: I7b0dd75d03819cab8e0cd4c29f0c1dc8d2e9c179
Reviewed-on: https://go-review.googlesource.com/34914
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Matthew Dempsky 2017-01-06 12:25:32 -08:00
parent 41d2278eef
commit 116da1c64a
2 changed files with 5 additions and 131 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

51
src/net/addrselect.go
View File

@ -188,33 +188,17 @@ func (s *byRFC6724) Less(i, j int) bool {
// Rule 9: Use longest matching prefix.
// When DA and DB belong to the same address family (both are IPv6 or
// both are IPv4): If CommonPrefixLen(Source(DA), DA) >
// both are IPv4 [but see below]): If CommonPrefixLen(Source(DA), DA) >
// CommonPrefixLen(Source(DB), DB), then prefer DA. Similarly, if
// CommonPrefixLen(Source(DA), DA) < CommonPrefixLen(Source(DB), DB),
// then prefer DB.
da4 := DA.To4() != nil
db4 := DB.To4() != nil
if da4 == db4 {
//
// However, applying this rule to IPv4 addresses causes
// problems (see issues 13283 and 18518), so limit to IPv6.
if DA.To4() == nil && DB.To4() == nil {
commonA := commonPrefixLen(SourceDA, DA)
commonB := commonPrefixLen(SourceDB, DB)
// CommonPrefixLen doesn't really make sense for IPv4, and even
// causes problems for common load balancing practices
// (e.g., https://golang.org/issue/13283). Glibc instead only
// uses CommonPrefixLen for IPv4 when the source and destination
// addresses are on the same subnet, but that requires extra
// work to find the netmask for our source addresses. As a
// simpler heuristic, we limit its use to when the source and
// destination belong to the same special purpose block.
if da4 {
if !sameIPv4SpecialPurposeBlock(SourceDA, DA) {
commonA = 0
}
if !sameIPv4SpecialPurposeBlock(SourceDB, DB) {
commonB = 0
}
}
if commonA > commonB {
return preferDA
}
@ -404,28 +388,3 @@ func commonPrefixLen(a, b IP) (cpl int) {
}
return
}
// sameIPv4SpecialPurposeBlock reports whether a and b belong to the same
// address block reserved by the IANA IPv4 Special-Purpose Address Registry:
// http://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
func sameIPv4SpecialPurposeBlock(a, b IP) bool {
a, b = a.To4(), b.To4()
if a == nil || b == nil || a[0] != b[0] {
return false
}
// IANA defines more special-purpose blocks, but these are the only
// ones likely to be relevant to typical Go systems.
switch a[0] {
case 10: // 10.0.0.0/8: Private-Use
return true
case 127: // 127.0.0.0/8: Loopback
return true
case 169: // 169.254.0.0/16: Link Local
return a[1] == 254 && b[1] == 254
case 172: // 172.16.0.0/12: Private-Use
return a[1]&0xf0 == 16 && b[1]&0xf0 == 16
case 192: // 192.168.0.0/16: Private-Use
return a[1] == 168 && b[1] == 168
}
return false
}

85
src/net/addrselect_test.go
View File

@ -117,27 +117,6 @@ func TestSortByRFC6724(t *testing.T) {
},
reverse: false,
},
// Prefer longer common prefixes, but only for IPv4 address
// pairs in the same special-purpose block.
{
in: []IPAddr{
{IP: ParseIP("1.2.3.4")},
{IP: ParseIP("10.55.0.1")},
{IP: ParseIP("10.66.0.1")},
},
srcs: []IP{
ParseIP("1.2.3.5"),
ParseIP("10.66.1.2"),
ParseIP("10.66.1.2"),
},
want: []IPAddr{
{IP: ParseIP("10.66.0.1")},
{IP: ParseIP("10.55.0.1")},
{IP: ParseIP("1.2.3.4")},
},
reverse: true,
},
}
for i, tt := range tests {
inCopy := make([]IPAddr, len(tt.in))
@ -268,67 +247,3 @@ func TestRFC6724CommonPrefixLength(t *testing.T) {
}
}
func mustParseCIDRs(t *testing.T, blocks ...string) []*IPNet {
res := make([]*IPNet, len(blocks))
for i, block := range blocks {
var err error
_, res[i], err = ParseCIDR(block)
if err != nil {
t.Fatalf("ParseCIDR(%s) failed: %v", block, err)
}
}
return res
}
func TestSameIPv4SpecialPurposeBlock(t *testing.T) {
blocks := mustParseCIDRs(t,
"10.0.0.0/8",
"127.0.0.0/8",
"169.254.0.0/16",
"172.16.0.0/12",
"192.168.0.0/16",
)
addrs := []struct {
ip IP
block int // index or -1
}{
{IP{1, 2, 3, 4}, -1},
{IP{2, 3, 4, 5}, -1},
{IP{10, 2, 3, 4}, 0},
{IP{10, 6, 7, 8}, 0},
{IP{127, 0, 0, 1}, 1},
{IP{127, 255, 255, 255}, 1},
{IP{169, 254, 77, 99}, 2},
{IP{169, 254, 44, 22}, 2},
{IP{169, 255, 0, 1}, -1},
{IP{172, 15, 5, 6}, -1},
{IP{172, 16, 32, 41}, 3},
{IP{172, 31, 128, 9}, 3},
{IP{172, 32, 88, 100}, -1},
{IP{192, 168, 1, 1}, 4},
{IP{192, 168, 128, 42}, 4},
{IP{192, 169, 1, 1}, -1},
}
for i, addr := range addrs {
for j, block := range blocks {
got := block.Contains(addr.ip)
want := addr.block == j
if got != want {
t.Errorf("%d/%d. %s.Contains(%s): got %v, want %v", i, j, block, addr.ip, got, want)
}
}
}
for i, addr1 := range addrs {
for j, addr2 := range addrs {
got := sameIPv4SpecialPurposeBlock(addr1.ip, addr2.ip)
want := addr1.block >= 0 && addr1.block == addr2.block
if got != want {
t.Errorf("%d/%d. sameIPv4SpecialPurposeBlock(%s, %s): got %v, want %v", i, j, addr1.ip, addr2.ip, got, want)
}
}
}
}