I think that I shall never see
a graph more lovely than a tree.
A tree whose crucial property
is loop-free connectivity.
A tree that must be sure to span
so packet can reach every LAN.
First, the root must be selected.
By ID, it is elected.
Least-cost paths from root are traced.
In the tree, these paths are placed.
A mesh is made by folks like me,
then bridges find a spanning tree.
вторник, 25 июня 2013 г.
Algorithm of Spanning Tree Protocol
Headers, MTU and MSS
HEADERS (bytes):
tcp=20
udp=8
ip=20
eth=18 (without vlan tag, DA(6)+SA(6)+FrameType(2)+FCS/CRC(4)=18)
eth=18 (without vlan tag, DA(6)+SA(6)+FrameType(2)+FCS/CRC(4)=18)
eth=22 (with vlan tag, DA(6)+SA(6)+802.1q-tag(4)+FrameType(2)+FCS/CRC(4)=22)
data=46-1500, MAX Ethernet frame=1518/1522, 802.3 MTU=1492
Full physical frame is Preambula(8)+Ethernet frame(802.3)+interframe gap(12)=1538/15
eth-payload=1500
data=46-1500, MAX Ethernet frame=1518/1522, 802.3 MTU=1492
Full physical frame is Preambula(8)+Ethernet frame(802.3)+interframe gap(12)=1538/15
eth-payload=1500
gre=4
nvgre=8
vlanid=4
vxlan=8
nvgre=8
vlanid=4
vxlan=8
mgre=4
esp=20
NAT-T udp=12
ppp=2
pppoe=6
l2tp=16
Ethernet (802.3)
eth:ip:tcp:data
MTU=1500
MSS=1500-8=1492
VXLAN
eth:ip:udp:vxlan:original-eth-without-vlan
MTU=20+8+8+(18+1500)=1554
NVGRE
eth:ip:nvgre:original-eth-with-vlan
MTU=20+8+(22+1500)=1550
eth:ip:tcp:data
MTU=1500
MSS=1500-8=1492
VXLAN
eth:ip:udp:vxlan:original-eth-without-vlan
MTU=20+8+8+(18+1500)=1554
NVGRE
eth:ip:nvgre:original-eth-with-vlan
MTU=20+8+(22+1500)=1550
"Classic" VPN Site-to-Site Connection Using IPsec Tunnel Mode
eth:ip:esp:ip:tcp:data
Cisco's IPsec Virtual Tunnel Interface (VTI)s
eth:ip:esp:ip:tcp:data
MTU=1460
MSS=1440
Point-to-Point GRE Tunnels
eth:ip:gre:ip:tcp:data
MTU=1476
MSS=1436
Point-to-Point GRE Tunnels + IPsec: ESP in Tunnel Mode
eth:ip:esp:ip:gre:ip:tcp:data
MTU=1500-(20+20+20+4)=1436
MSS=1396
Point-to-Point GRE Tunnels + IPsec: ESP in Transport Mode
eth:ip:esp:gre:ip:tcp:data
MTU=1456
MSS=1416
Point-to-Multipoint mGRE Tunnels + IPsec: ESP in Transport Mode
eth:ip:esp:mgre:ip:tcp:data
MTU=1500-(20+20+4)=1456
MSS=1416
L2TP/IPsec: ESP in Transport Mode
eth:ip:esp:udp:l2tp:ppp:ip:tcp:data
MTU=1500-(20+20+8+16+2)=1434
MSS=1404
L2TP/IPsec: ESP in Transport Mode, NAT-T
eth:ip:NAT-T udp:esp:udp:l2tp:ppp:ip:tcp:data
MTU=1500-(20+12+20+8+16+2)=1422
MSS=MTU-40=1382
L2TP:
eth:ip:udp:l2tp:ppp:ip:tcp:data
MTU=1454
MSS=1434
PPPoE:
eth:pppoe:ppp:ip:tcp:data
MTU=1492
MSS=1452
PPTP:
eth:ip:gre:ppp:ip:tcp:data
MTU=1474
MSS=1434
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