11. Given real numbers $x_{1}, x_{2}, x_{3}$ satisfy: $x_{1}^{2}+x_{2}^{2}+x_{3}^{2}+x_{1} x_{2}+x_{2} x_{3}=2$, then the maximum value of $\left|x_{2}\right|$ is $\qquad$
$$
\begin{array}{l}
4=2 x_{1}^{2}+2 x_{2}^{2}+2 x_{3}^{2}+2 x_{1} x_{2}+2 x_{2} x_{3}=x_{1}^{2}+\left(x_{1}+x_{2}\right)^{2}+x_{3}^{2}+\left(x_{2}+x_{3}\right)^{2} \\
\geqslant \frac{\left(-x_{1}+x_{1}+x_{2}\right)^{2}}{2}+\frac{\left(-x_{3}+x_{2}+x_{3}\right)^{2}}{2}=x_{2}^{2} \Rightarrow x_{2}^{2} \leqslant 4,
\end{array}
$$

When the equality holds, $\left\{\begin{array}{l}-x_{1}=x_{1}+x_{2}, \\ -x_{3}=x_{2}+x_{3}\end{array} \Rightarrow x_{2}=2, x_{1}=x_{3}=-1\right.$. Therefore, the maximum value of $\left|x_{2}\right|$ is 2.