diff --git a/chapter/layer3.tex b/chapter/layer3.tex
index f787f92..23eba4a 100644
--- a/chapter/layer3.tex
+++ b/chapter/layer3.tex
@@ -94,7 +94,7 @@ both protocols being defined in the late 1980s.
 
 \gls{isis} had a stable implementation up through the 1990s and became the 
 standard of the era in \gls{isp} networks. Where as \gls{ospf} remained largely 
-the standard in medium-large enterprise networks.
+the standard in medium-large enterprise networks.\cite{JuniperKatz2000:online}
 
 Today in late 2010s. Many of the things that made the difference is being 
 considered being largely irrelevant. Both because computing hardware has come a