Warning
This is an unpolished draft of the second edition of this ebook. If you find any error or have suggestions to improve the text, please create an issue via https://github.com/obonaventure/cnp3/issues?milestone=2
Ethernet networks¶
- With the 802.1d protocol, Ethernet switches exchange BPDUs that contain four informations :
- the Root identifier
- the Cost to reach the root
- the Transmitter identifier
The third information contains two parts : the identifier of the switch that sent the BPDU and the identifier of the port where the BPDU has been sent. Each switch uses a unique identifier for each of its ports.
[R=123,C=11,T=16.9]
[R=122,C=21,T=19]
[R=123,C=17,T=15.1]
[R=123,C=17,T=12.19]
[R=126,C=11,T=6.9]
[R=123,C=21,T=19]
[R=123,C=17,T=25.1]
[R=123,C=17,T=22.19]
Consider a large Ethernet network that contains the switches shown in the figure below.
![\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{switch/.style = {diamond, draw, text centered, minimum height=2em, node distance=2cm}, }
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
[node distance= 4cm and 4cm]
\node[switch] (S32) {S32};
\node[switch, left of=S32] (S22) {S22};
\node[switch, right of=S32] (S19) {S19};
\node[switch, above of=S32] (S42) {S42};
\node[switch, below of=S32] (S25) {S25};
\node[switch, right of=S25] (S46) {S46};
\path[draw,thick]
(S32) edge (S22)
(S32) edge (S19)
(S32) edge (S42)
(S32) edge (S25)
(S32) edge (S46);](_images/tikz-4f51659d8d9c4ec34f126d36651d48dce48be50d.png)
Switch 32 has received the following BPDUs from its neighbours :
- [R=9,C=21,T=19.2]
- [R=9,C=12,T=42.1]
- [R=25,C=5,T=25.2]
- [R=9,C=5,T=46.3]
[R=25,C=6,T=25]
[R=9,C=6,T=25]
[R=9,C=6,T=19.32]
[R=9,C=5,T=32]
- Consider the same network as above. Assume now that switch 32 has received the following BPDUs from its neighbours :
- [R=9,C=6,T=19.2]
- [R=9,C=12,T=42.1]
- [R=9,C=5,T=25.2]
- [R=9,C=5,T=46.3]
Consider the switched network shown in the figure below.
![\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{switch/.style = {diamond, draw, text centered, minimum height=2em, node distance= 2cm}, }
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[switch] (S3) {S3};
\node[switch, left of=S3] (S6) {S6};
\node[switch, right of=S3] (S7) {S7};
\node[switch, above of=S3] (S4) {S4};
\node[switch, below of=S3] (S9) {S9};
\path[draw,thick]
(S3) edge (S6)
(S3) edge (S7)
(S6) edge (S4)
(S4) edge (S7)
(S3) edge (S9)
(S9) edge (S7)
(S3) edge (S7);](_images/tikz-53fd3eadb45196fe84be1273cd1b72091bcb18ca.png)
- Consider the same network as in the above question.
The port of S3 that leads to S6 is in the designated state.
The port of S3 that leads to S9 is in the designated state.
The port of S3 that leads to S7 is in the designated state.
The port of S6 that leads to S4 is in the blocked state.
The port of S7 that leads to S4 is in the blocked state.
The port of S7 that leads to S9 is in the blocked state.
The port of S4 that leads to S6 is in the designated state.
The port of S4 that leads to S7 is in the designated state.
The port of S9 that leads to S7 is in the designated state.
Ethernet switches can also be connected to a HUB. Consider the Ethernet network below.
![\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{switch/.style = {diamond, draw, text centered, minimum height=2em, node distance= 2cm}, }
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{hub/.style = {circle, draw, text centered, minimum height=2em, node distance=2cm}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[switch] (S9) {S9};
\node[switch, left of=S9] (S12) {S12};
\node[switch, right of=S9] (S6) {S6};
\node[switch, above of=S9] (S3) {S3};
\node[hub, below of=S9] (HUB) {HUB};
\path[draw,thick]
(S3) edge (S12)
(S12) edge (HUB)
(S6) edge (S3)
(S6) edge (HUB)
(S3) edge (S9)
(S9) edge (HUB);](_images/tikz-08ffdd694acbb09080d5fc9a2cfaa36e09bf34ca.png)
The port of switch 12 attached to the Hub is a designated port.
The port of switch 9 attached to the Hub is a designated port.