How to show circle on two edges to show PC, VPC connection

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1

I am trying to generate the network topology diagrams and wanted to show circle on two edges to show the PC, VPC connections. Please help me
Screenshot 2022-08-04 at 10.16.41 AM

2

The big trick is to use a colorlist (colorList | Graphviz) to guarantee parallel lines. Two “white” lines are in the list to produce greater separation between the two black lines.

graph P{
  splines=false
  ranksep= .25
  node [shape=rect]
  A B
  // sizing set by eyeball
  C1  [shape=ellipse width=.35 height=.2 fixedsize=true label=""]
  // each edge is drawn as two black lines, separated by two "white" lines
  edge [color="black:white:white:black"]
  A -- C1 -- B
}

Giving:
parallelEdges0

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