Public/ConvertFrom-BgpMessage.ps1
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function ConvertFrom-BgpMessage { <# .SYNOPSIS Parses a BGP message byte[] (OPEN with capabilities, UPDATE, NOTIFICATION, KEEPALIVE). .PARAMETER TwoOctetAs Parse AS_PATH with 2-byte ASNs (peer did not negotiate the 4-octet AS capability). #> [CmdletBinding()] param( [Parameter(Mandatory, ValueFromPipeline)][byte[]]$Message, [switch]$TwoOctetAs ) process { if ($Message.Length -lt 19) { throw 'Message shorter than the 19-byte BGP header.' } $typeName = switch ([int]$Message[18]) { 1 { 'OPEN' } 2 { 'UPDATE' } 3 { 'NOTIFICATION' } 4 { 'KEEPALIVE' } 5 { 'ROUTE-REFRESH' } default { 'UNKNOWN' } } $r = [ordered]@{ PSTypeName = 'PowerBGP.Message' Type = $typeName Length = [int](Get-NetUInt $Message 16 2) MarkerValid = (@($Message[0..15] | Where-Object { $_ -ne 0xFF }).Count -eq 0) Summary = '' } if ($typeName -eq 'OPEN' -and $Message.Length -ge 29) { $caps = @() $o = 29 $end = [Math]::Min(29 + $Message[28], $Message.Length) while ($o + 2 -le $end) { $ptype = $Message[$o]; $plen = $Message[$o + 1] if ($ptype -eq 2) { $c = $o + 2; $cend = [Math]::Min($c + $plen, $Message.Length) while ($c + 2 -le $cend) { $code = [int]$Message[$c]; $cl = [int]$Message[$c + 1] $val = if ($cl -and ($c + 1 + $cl) -lt $Message.Length) { $Message[($c + 2)..($c + 1 + $cl)] } else { @() } $name = $script:BgpCapNames[$code]; if (-not $name) { $name = "Capability $code" } $caps += [pscustomobject]@{ Code = $code; Name = $name; Value = (($val | ForEach-Object { '{0:X2}' -f $_ }) -join '') } $c += 2 + $cl } } $o += 2 + $plen } $r.Version = [int]$Message[19] $r.MyAs = [int](Get-NetUInt $Message 20 2) $r.HoldTime = [int](Get-NetUInt $Message 22 2) $r.RouterId = [ipaddress]::new([byte[]]$Message[24..27]) $r.Capabilities = $caps $as4 = $caps | Where-Object Code -EQ 65 | Select-Object -First 1 $r.Asn = if ($as4 -and $as4.Value.Length -eq 8) { [uint32][Convert]::ToUInt32($as4.Value, 16) } else { [uint32]$r.MyAs } $r.Summary = 'AS {0} hold {1} id {2} caps [{3}]' -f $r.Asn, $r.HoldTime, $r.RouterId, (($caps | ForEach-Object Name) -join ', ') } elseif ($typeName -eq 'NOTIFICATION' -and $Message.Length -ge 21) { $r.ErrorCode = [int]$Message[19] $r.ErrorSubcode = [int]$Message[20] $r.ErrorName = $script:BgpNotifyErrors[[int]$Message[19]] $r.Data = if ($Message.Length -gt 21) { [byte[]]$Message[21..($Message.Length - 1)] } else { [byte[]]@() } $r.Summary = '{0} ({1}/{2})' -f $r.ErrorName, $r.ErrorCode, $r.ErrorSubcode } elseif ($typeName -eq 'UPDATE' -and $Message.Length -ge 23) { $wlen = [int](Get-NetUInt $Message 19 2) $wEnd = 21 + $wlen $withdrawn = @(Read-BgpPrefix $Message 21 $wEnd) $alen = [int](Get-NetUInt $Message $wEnd 2) $aStart = $wEnd + 2; $aEnd = $aStart + $alen if ($aEnd -gt $Message.Length) { throw 'UPDATE attribute length exceeds message.' } $attrs = @() $o = $aStart while ($o + 3 -le $aEnd) { $flags = [int]$Message[$o]; $code = [int]$Message[$o + 1] if ($flags -band 0x10) { $vl = [int](Get-NetUInt $Message ($o + 2) 2); $vs = $o + 4 } else { $vl = [int]$Message[$o + 2]; $vs = $o + 3 } $val = if ($vl) { [byte[]]$Message[$vs..($vs + $vl - 1)] } else { [byte[]]@() } $attrs += [pscustomobject]@{ Flags = $flags; Code = $code; Value = $val } $o = $vs + $vl } $r.Withdrawn = $withdrawn $r.Nlri = @(Read-BgpPrefix $Message $aEnd $Message.Length) $r.Attributes = $attrs $r.Origin = $null; $r.AsPath = @(); $r.NextHop = $null; $r.Med = $null; $r.LocalPref = $null; $r.Community = @() foreach ($a in $attrs) { switch ($a.Code) { 1 { if ($a.Value.Length) { $r.Origin = $script:BgpOrigins[[int]$a.Value[0]] } } 2 { $w = if ($TwoOctetAs) { 2 } else { 4 } $p = 0; $path = @() while ($p + 2 -le $a.Value.Length) { $cnt = [int]$a.Value[$p + 1]; $p += 2 for ($k = 0; $k -lt $cnt; $k++) { $path += [uint32](Get-NetUInt $a.Value $p $w); $p += $w } } $r.AsPath = $path } 3 { if ($a.Value.Length -eq 4) { $r.NextHop = [ipaddress]::new($a.Value) } } 4 { $r.Med = [uint32](Get-NetUInt $a.Value 0 4) } 5 { $r.LocalPref = [uint32](Get-NetUInt $a.Value 0 4) } 8 { for ($k = 0; $k + 4 -le $a.Value.Length; $k += 4) { $r.Community += '{0}:{1}' -f (Get-NetUInt $a.Value $k 2), (Get-NetUInt $a.Value ($k + 2) 2) } } 14 { if ($a.Value.Length -ge 5) { $afi = [int](Get-NetUInt $a.Value 0 2) $nhLen = [int]$a.Value[3] if ($a.Value.Length -ge (4 + $nhLen + 1)) { if (-not $r.NextHop -and $nhLen -in 4, 16, 32) { $r.NextHop = [ipaddress]::new([byte[]]$a.Value[4..(3 + [Math]::Min($nhLen, 16))]) } $mpBytes = [byte[]]$a.Value $r.Nlri += @(Read-BgpPrefix $mpBytes (5 + $nhLen) $mpBytes.Length $afi) } } } 15 { if ($a.Value.Length -ge 3) { $afi = [int](Get-NetUInt $a.Value 0 2) $mpBytes = [byte[]]$a.Value $r.Withdrawn += @(Read-BgpPrefix $mpBytes 3 $mpBytes.Length $afi) } } } } $parts = @() if ($r.Nlri.Count) { $parts += "NLRI $($r.Nlri -join ',')"; $parts += "NH $($r.NextHop)"; $parts += "AS_PATH $($r.AsPath -join ' ')" } if ($r.Withdrawn.Count) { $parts += "WD $($r.Withdrawn -join ',')" } if (-not $parts) { $parts = 'End-of-RIB / empty' } $r.Summary = $parts -join '; ' } [pscustomobject]$r } } |